HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Echarte, L. Articles by Tollenaar, M. Search for Related Content PubMed Articles by Echarte, L. Articles by Tollenaar, M. Agricola Articles by Echarte, L. Articles by Tollenaar, M. Related Collections Crop Physiology & Metabolism Maize

CROP PHYSIOLOGY & METABOLISM

Kernel Set in Maize Hybrids and Their Inbred Lines Exposed to Stress

Dep. of Plant Agriculture, Crop Science Building, Univ. of Guelph, Guelph, ON, Canada, N1G 2W1. Financial support, in part, from the Ontario Ministry of Agriculture and Food, Natural Science and Engineering Research Council, and Ontario Corn Producers' Association. L. Echarte was supported by a postgraduate scholarship from OAS

^* Corresponding author (lecharte{at}mdp.edu.ar)

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Heterosis for grain yield in maize (Zea mays L.) has been associated with heterosis for kernel number. The objective of this study was to elucidate physiological traits underlying the superior kernel no. establishment in hybrids in comparison with that in their inbred lines, using the relationship between kernel no. plant^–1 (KN_P) and plant growth rate during the critical period of approximately 30 d bracketing silking (PGR_S). Experiments were performed at the Arkell Research Station near Guelph, ON, Canada, during 2003 and 2004. Maize was grown at three levels of water availability (100, 75, or 60% of daily transpiration) during a period bracketing silking and at two plant densities (6 and 10 plants m^–2) without nutrient limitations to generate a range of levels of resource availability plant^–1. Kernel no. plant^–1 was greater in the hybrids than in their parental inbred lines at all levels of resource availability, which was attributable mainly to a greater kernel set per unit PGR_S in the hybrids. Greater kernels set per unit PGR_S in hybrids vs. their inbred lines resulted from one or more of the following features: (i) low threshold of PGR_S for kernel set, (ii) high kernel set response to PGR_S increments at low resource availability plant^–1, and (iii) high potential kernel number. Heterosis for kernel set was associated with heterosis for ear growth rate during the critical period for kernel set bracketing silking (EGR_s) to varying degrees, and the extent of the association varied with inbred line–hybrid combination and level of resource availability plant^–1.

Abbreviations: DM, dry matter • EGR_S, ear growth rate during the critical period for kernel set bracketing silking • GDD, growing degree-day • KN_P, kernel no. plant^–1 • LAI, leaf area index • PGR_S, plant growth rate during the critical period for kernel set bracketing silking

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
HETEROSIS FOR GRAIN YIELD in maize is associated with heterosis for kernel no. (Leng, 1954; Sinha and Khanna, 1975; Tollenaar et al., 2004). The term heterosis refers to the superiority in performance of the F1 hybrid over either one of its parents (Shull, 1908). Heterosis for grain yield in maize has been associated with four physiological processes: (i) heterosis for leaf area index (LAI) due to increased leaf size, resulting in increased light interception and dry matter (DM) accumulation of hybrids; (ii) heterosis for stay green, which in addition to heterosis for maximum LAI, results in increased light interception and DM accumulation during the grain-filling period; (iii) heterosis for sustaining photosynthesis of green leaf area during the grain-filling period, resulting in increased canopy photosynthesis during this period; and (iv) heterosis for harvest index that was due, in part, to a heterosis for kernel no. (Tollenaar et al., 2004). The physiological mechanisms underlying the heterosis for kernel no. and its response to stress are not known.

Kernel no. plant^–1 is associated with PGR_S (Tollenaar and Daynard, 1978; Fischer and Palmer, 1984; Aluko and Fischer, 1988; Andrade et al., 1999). In maize, the KN_P–PGR_S relationship has been described by two successive curves to account for the first and second ear in prolific, or a single curve in nonprolific plants (Tollenaar et al., 1992; Andrade et al., 1999; Echarte et al., 2004). Features of the KN_P–PGR_S relationship are (i) a PGR_S threshold for kernel set at low plant growth rates, (ii) kernel set response with increasing PGR_S at low and moderated PGR_S (i.e., initial slope of the KN_P–PGR_S relationship), and (iii) the value of the asymptote at high PGR_S, that is, potential KN_p (Tollenaar et al., 1992; Andrade et al., 1999; Vega et al., 2001; Echarte et al., 2004). The greater kernel no. in hybrids compared with that in their parental inbred lines could be associated with greater PGR_S and/or with any of the three features of the KN_P–PGR_S relationship.

The relationship between KN_P and PGR_S for older and newer maize hybrids was previously analyzed by Tollenaar et al. (1992) and Echarte et al. (2004). Results of the two studies differed for the threshold PGR_S for kernel set and the initial slope of the KN_P–PGR_S relationship. The differences might be attributable to the difference in methodology employed in the two studies: results were based on whole-plot means in Tollenaar et al. (1992) and on individual plants in Echarte et al. (2004). Reanalysis of the data in the latter study using plot means rather than individual plant data confirmed that methodology can have an influence on the results (Echarte, 2004, unpublished data). A wide range of values for PGR_S and KN_P are obtained when using individual plants rather than plot means, allowing for a more precise estimate of the threshold PGR_S for kernel set.

Both DM partitioning to the ear and kernel set per unit EGR_S may be involved in differences in kernel set between hybrids and their parental inbred lines (Andrade et al., 2000). Echarte et al. (2004) reported that the greater kernel set of newer vs. older maize hybrids was related to a greater DM partitioning to the ear rather than to a greater kernel set per unit ear growth.

In this study, we examine physiological traits (i.e., plant growth rate and EGR_S) and their association with the greater kernel no. in hybrids than in their parental inbred lines. We quantify PGR_S and the three features of the KN_P–PGR_S relationship in two hybrids and their parental inbred lines using water stress and plant density stress to generate a range in PGR_S values. We analyze the data based on individual plants to better estimate the parameters of the KN_P–PGR_S relationship. In addition, we examined to what extent kernel set is associated with DM partitioning to the ear during the critical period bracketing silking in hybrids and their parental inbred lines.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Plant Material, Experimental Design, and Treatments
The maize hybrids CG60 x CG102 and CG60 x MBS1236 and their parental inbred lines CG60, CG102, and MBS1236 were grown at the Arkell Research Station near Guelph, ON (43°39' N, 80°25' W and 375 m above sea level), using a hydroponic system in the field (Tollenaar and Migus, 1984) during the 2003 and 2004 growing seasons. Plants were grown in 22.5-L plastic pails filled with turface, a baked montmorillonite clay (International Minerals and Chemical, Blue Mountain, MS) and irrigated four times a day using a nutrient solution as described by Tollenaar (1989). A timer controlled application of nutrient solution to the pails. The duration of the application was set such that nutrient solution drained from the bottom of all pails. Weeds were effectively controlled by hand. Genotypes were compared in four experiments each involving a hybrid and its two parental inbred lines, one season, and one type of stress. Experiments 1 and 2 included the inbred lines CG60, CG102, and their hybrid CG60 x CG102 exposed to various water availability levels during 2003 (Exp. 1) and 2004 (Exp. 2). Experiments 3 and 4 included the inbred lines CG60, MBS1236, and their hybrid CG60 x MBS1236 exposed to various water availability levels (Exp. 3) and plant densities (Exp. 4) during 2004. Water availability levels during the period bracketing silking and plant density were used as the source of experimental variation for KN_P and PGR_S. The experimental design was a split-plot complete-block design with three replications, with genotypes as main plots and water availability or plant density as a subplot. Inbred lines and hybrids were planted in adjacent blocks to avoid competition effects. Pails were over sown and thinned at V3 (Ritchie and Hanway, 1982) to 2 or 5 plants pail^–1. In the water stress experiments (Exp. 1, 2, and 3) and in the low plant density treatment in Exp. 4, subplots comprised six 8.5-m long rows, and the distance between rows was 0.95 m. Plant density at harvest was 6 plants m^–2. In the high plant density treatment in Exp. 4, subplots comprised six 4-m long rows and the distance between rows was 1.45 m (i.e., the greater row width in this treatment was a consequence of limitations in the availability of pails arranged in 0.95-m row widths). Plant density at harvest was 10 plants m^–2.

Water Stress Experiment
The water stress treatment was designed such that water stress was a function of water demand by the plant (i.e., plant transpiration) rather than water supply, because genotypes varied substantially in leaf area plant^–1 (data not shown). Individual plants were supplied with 100% of the daily transpiration (control), or with either 75 or 60% of daily transpiration (treatments) from 3 to 9 d before silking until 13 d after silking of the control. The daily transpiration of control plants was estimated as

where, P_c represents the pail water holding capacity and P_c+1d represents the pail water content 24 h after supplying the pail with nutrient solution. For each genotype, P_c was estimated in eight control pails by supplying the pails with excess nutrient solution and weighing the pails immediately after the drainage from the bottom of the pails was finished and P_c+1d was estimated by weighing the pails in the morning before supplying them with excess nutrient solution. All pails involved in the water stress study were covered with plastic bags during the treatment period to prevent precipitation to confound the estimation of daily plant transpiration. Normal irrigation of all pails was reestablished after the end of the treatment period for each genotype.

Measurements
Silking dates were recorded for each genotype as the dates when 50% of the plants (total n = 36 plants treatment^–1 genotype^–1) presented at least one emerged silk from the husks. Potential kernel no. was assessed in 20 border plants genotype^–1 at silking during 2004 as the product of kernel rows ear^–1 and spikelets row^–1, plus the no. of spikelets in the tip (the tip was defined as the portion of the ear where the no. of kernel rows was less than that in the center of the ear). Shoot biomass of tagged plants was quantified at approximately 3 to 9 d before and 13 d after silking of the control plots for each genotype through a combination of destructive and nondestructive sampling, and KN_P was determined at maturity. Sampling date after silking was the same in all studies to get relevant estimates of ear biomass for the various treatments.

Destructive Sampling
Destructive sampling was performed to establish allometric relationships between morphometric variables, that is, basal stem diameter and diameter and length of the ear, and dry weights of shoot and ears. Morphometric variables were measured on 4 to 6 plants replicate^–1 for each treatment. Immediately after measurements, plants were harvested. Plants were separated into stem plus leaves plus tassel and ears, and were oven dried at 65°C until constant weight. Allometric relationships were established between morphometric variables and dry weights of shoot and ears using a stepwise regression procedure of SAS (SAS Institute, 1999). Ears included kernels and rachis. All equations were significant at P < 0.05, and average r² was 0.85 (Tables 1 and 2).

Data Analysis
Under the growing conditions of these experiments, all hybrids produced a single ear plant^–1, except the inbred line CG60 during 2003 (1.14 ears plant^–1). However, only nonprolific plants are included in the analyses. Growth rate during the critical period for kernel set was estimated as the quotient of accumulated biomass in shoots or topmost ear and the duration of the period in growing degree-days (GDDs). Growing degree-days were calculated from daily average temperatures above 8°C (Ritchie and NeSmith, 1991; Cirilo and Andrade, 1996) and accumulated during the period bracketing silking for each hybrid. We assumed a linear relationship between biomass accumulation per plant and GDDs during the treatment period bracketing silking, that ear biomass was negligible at 10 d before silking (i.e., at the start of the treatment period), and that differences in the duration of the treatment period (due to differences in the starting date of the treatment) did not affect the KN_P–PGR_S relationship. Silking dates of the control treatments occurred within 1 wk and within 12 d during 2003 and 2004, respectively. Mean daily irradiance and mean temperature values during the period bracketing silking were 17.7 MJ d^–1 and 20°C during 2003 and 16.2 MJ d^–1 and 17.6°C during 2004.

The relationships between KN_P and PGR_S and between KN_P and EGR_S were fitted with Model [1] (Jandel Scientific, 1991):

[1]

where x represents either PGR_S or EGR_S, and parameters a and b represent the initial slope and the curvilinearity of the KN_P–PGR_S or KN_P–EGR_S relationship, respectively. The variable x_t represents the highest value of either PGR_S or EGR_S at which KN_P = 0 (i.e., threshold values for kernel set). The regression of KN_P on PGR_S for genotypes with high KN_P variability (e.g., MBS 1236; Fig. 1 ) or genotypes with no KN_P values at high PGR_S (e.g., MBS1236 and CG102; Fig. 1) yielded nonbiologically meaningful values for parameters a and b (for example, a negative value for b which resulted in an exponential kernel no. increase with increasing PGR_S). Therefore, the KN_P–PGR_S relationship of these genotypes was fitted with a linear equation, Model [2] (Jandel Scientific, 1991):

[2]

where x and a represent PGR_S and the slope of the KN_P–PGR_S relationship, respectively. The variable x_t represents the PGR_S threshold for kernel set.

View larger version (34K): [in this window] [in a new window]   Fig. 1. Relationship between kernel no. plant–1 and plant growth rate during a period bracketing silking for two hybrids (CG60 x CG102 and CG60 x MBS1236) and their three parental inbred lines (CG60, CG102, and MBS1236) exposed to water stress (W, 2003 and 2004) and plant density stress (PD, 2004). r2 = 0.60, 0.46, and 0.53 for Model [1] fitted to CG60, CG60 x CG102, and CG60 x MBS1236, respectively; and r2 = 0.51 and 0.43 for Model [2] fitted to CG102 and MBS1236, respectively. GDD = growing degree-day.

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Heterosis for Kernel Number and Plant Growth Rate
Kernel no. plant^–1 was greater in the hybrids than in their parental inbred lines at all levels of water availability and both plant densities (P < 0.05, Table 3), but rate of plant DM accumulation during the silking period (PGR_S) of the hybrids was not consistently greater than that of their parental inbred lines (Table 3). Kernel no. plant^–1 is associated with PGR_S (Tollenaar et al., 1992; Andrade et al., 1999). In general, aboveground DM at silking is greater in hybrids than in their parental inbred lines (Sinha and Khanna, 1975; Tollenaar et al., 2004), even when plant density of hybrids and inbred lines were manipulated such that they had the same LAI and intercepted radiation (Djisbar and Gardner, 1989). Rate of DM accumulation around silking was also greater in hybrids than in inbred lines (Tollenaar et al., 2004), although maximum rate of photosynthesis per unit leaf area was not different between the two groups (Ahmadzadeh et al., 2004). Although it is not clear why PGR_S was not consistently greater in hybrids than in their inbred lines in this study, results clearly show that differences in KN_P among genotypes are not strictly a result of differences in PGR_S. These results are consistent with published reports that have shown that KN_p in improved tropical maize hybrids (Edmeades et al., 1993) and in newer Argentinean maize hybrids (Echarte et al., 2000) are not associated with greater PGR_S.

View larger version (20K): [in this window] [in a new window]   Fig. 2. Fitted equations to the relationship between kernel no. plant–1 and plant growth rate during a period bracketing silking depicted in Fig. 1, for (a) the hybrid CG60 x CG102 and its two parental inbred lines CG60 and CG102, and for (b) the hybrid CG60 x MBS1236 and its two parental inbred lines CG60 and MBS1236. GDD = growing degree-day.

View larger version (26K): [in this window] [in a new window]   Fig. 3. Frequency distributions of kernel no. plant–1 for plants with plant growth rate during the period for kernal set bracketing silking (PGRS) in the range 0.15 > PGRS > 0.19 g plant–1 GDD–1 for two hybrids (CG60 x CG102 and CG60 x MBS1236) and their three parental inbred lines (CG60, CG102, and MBS1236) exposed to water stress (W, 2003 and 2004) and plant density stress (PD, 2004).

The response of KN_P to increasing PGR_S at low resource availability per plant (i.e., for PGR_S > threshold value) was greater in the two hybrids and their common parental inbred line CG60 than in the inbred lines CG102 and MBS1236 (Fig. 1 and 2). This was indicated by a higher kernel set relative to their potential KN_P in the former genotypes (55, 67, and 69% for CG60, CG60 x CG102 and CG60 x MBS1236, respectively) than in the inbred lines CG102 and MBS1236 for which kernel set was 16 to 19% of the potential KN_P at moderate PGR_S (i.e., 0.2 to 0.3 g plant^–1 GDD^–1). Moreover, the last two inbred lines did not reach KN_P values similar to their potential KN_P at the highest PGR_S range explored (Fig. 1; Table 4).

The relationship between KN_P and PGR_S did not appear to be affected by the nature of the stress that was applied (i.e., water stress and plant density stress). No differences in the KN_P– PGR_S relationships were apparent using either water availability or plant density as source of variation (P > 0.05; Fig. 1) in the three genotypes for which fitted curvilinear equations to the KN_P–PGR_S data were possible (i.e., CG60, CG60 x CG102, and CG60 x MBS1236 in Exp. 3 and 4). In addition, KN_P did not differ between types of stress for any of the three genotypes at a particular range in PGR_S (P > 0.05) in 11 out of 12 comparisons (Table 4); KN_P differed only in the comparison between the two stresses for CG60 at PGR_S between 0.3 and 0.4 g plant^–1 GDD^–1. The similar KN_P response to PGR_S under different stress is consistent with a previous report based on plot means (Andrade et al., 2002) and it indicates that selection for increased water stress tolerance could be effectively achieved by selecting for genotypes that are tolerant to high plant density stress. In addition, these results confirm published reports that have suggested that there are common physiological mechanisms that confer general stress tolerance (Tollenaar and Wu, 1999; Bänziger et al., 2002; Echarte et al., 2004).

Kernel Number vs. Ear Growth Rate
The proportion of heterosis for KN_P that was associated with heterosis for EGR_S varied greatly among the inbred line–hybrid combinations examined in this study. EGR_S of the hybrid CG60 x CG102 was generally greater than that of its parental inbred lines and EGR_S of the hybrid CG60 x MBS1236 was greater than that of CG60, but EGR_S of the hybrid CG60 x MBS1236 was lower than that of MBS1236 in most cases (P < 0.05; Table 6). KN_P per unit EGR_S was greater in the hybrids CG60 x CG102 and CG60 x MBS1236 than in their inbred lines (P < 0.05; Fig. 4 ). An exception to this general trend was the lack of difference in KN_P per unit EGR_S between CG60 and CG60 x MBS1236 at a low EGR_S interval (i.e., 0–0.02 g ear^–1 GDD^–1). The proportion of heterosis for KN_P that was associated with heterosis for ear growth rate at low and high resource availability is illustrated in Fig. 5 . For the inbred line–hybrid combination CG60 and CG60 x CG102, the increase in KN_P that was associated with EGR_S increments (i.e., AB) represented 29 to 32% of the total increase in KN_P (i.e., AC) at both low and at high PGR_S (Fig. 5). For the inbred line–hybrid combination CG60 and CG60 x MBS1236, the increase in KN_P that was associated with EGR_S increments was 64% at low PGR_S and 32% at high PGR_S (Fig. 5). In contrast, the increase in kernel set in the hybrid CG60 x MBS1236 over the inbred line MBS1236 was not related to EGR_S increments (Table 6). Therefore, the relative effect of heterosis for EGR_S (or increased partitioning to the ear) on kernel set increments varied with the particular inbred line–hybrid combination and the level of resource availability per plant.

View larger version (35K): [in this window] [in a new window]   Fig. 4. Relationship between kernel no. plant–1 and ear growth rate during a period bracketing silking for two hybrids (CG60 x CG102 and CG60 x MBS1236) and their three parental inbred lines (CG60, CG102, and MBS1236) exposed to water stress (W, 2003 and 2004) and plant density stress (PD, 2004). r2 = 0.74, 0.75, 0.72, and 0.63 for Model [1] fitted to CG102, CG60, CG60 x CG102, and CG60 x MBS1236, respectively; and r2 = 0.54 for Model [2] fitted to MBS1236. GDD = growing degree-day.

View larger version (23K): [in this window] [in a new window]   Fig. 5. The proportion of the difference in kernel no. plant–1 (KNP) between the inbred line CG60 and the hybrids (a) CG60 x CG102 and (b) CG60 x MBS1236 that is associated with ear growth rate during the period bracketing silking (EGRS). Open symbols indicate values of KNP and EGRS at a PGRS interval from 0.1 to 0.2 g plant–1 GDD–1 (GDD = growing degree-day; and for CG60 and the hybrids, respectively). Closed symbols indicate values of KNP and EGRS at a PGRS interval from 0.3 to 0.4 g plant–1 GDD–1 ( and for CG60 and the hybrids, respectively). The total difference in KNP between the inbred line CG60 and the hybrid is equal to AC and the proportion of the difference in KNP that is associated with the difference in EGRS is equal to AB/AC.

Desirable Features of Inbred Lines
The identification of pairs of inbred lines with superior yield performance in single-cross combination is a major weakness of maize breeding programs (Gama and Hallauer, 1977; Hallauer et al., 1988; Dudley et al., 1992; Samanci, 1996; Tokatlidis, 2000; Shieh and Thseng, 2002). Our results show that greater KN_P per unit PGR_S in the hybrids than in their parental inbred lines is associated with a low threshold of PGR_S for kernel set, a high kernel set response with increasing PGR_S at low resource availability per plant, and a high potential kernel number. Heterosis for kernel set appears to be the result of a combination of the favorable features of the KN_P–PGR_S relationship of the parental inbred lines at all levels of resource availability. For example, the two hybrids showed low PGR_S thresholds for kernel set and high kernel set response to PGR_S increments similar to those of their parental inbred line CG60 (Fig. 1 and 2) and high potential KN_P similar to those of their parental inbred lines CG102 or MBS1236. One could speculate that a combination of two inbred lines that both have a high PGR_S threshold for kernel set and a low kernel set response to PGR_S increments at low resource availability per plant may result in a low yielding hybrid. The detection of inbred lines with desirable features of the KN_P–PGR_S relationship (i.e., low PGR_S threshold for kernel set, high kernel set response to PGR_S increments at low resource availability per plant, and high kernel set potential) could add efficiency to the development of maize hybrids that perform well under optimal and stress conditions. The potential impact of the male and the female parent on the heterotic response should be addressed in future studies.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Kernel set in maize is a function of PGR_S (Tollenaar et al., 1992) and partitioning of DM to the ear during the period bracketing silking (Edmeades et al., 1993; Echarte et al., 2004). Results in this study showed that KN_p was greater in the hybrids than in their parental inbred lines at all levels of resource availability, even though PGR_S was not always greater in hybrids than in their parental inbred lines. The difference in kernel no. was attributable mainly to a greater kernel set per unit PGR_S which resulted from (i) a low threshold of PGR_S for kernel set, (ii) a high kernel set response to PGR_S increments at low resource availability per plant, and (iii) a high potential KN_p. Although kernel set was described well by the KN_P–PGR_S relationship in the two hybrids and one of the three inbred lines, the KN_P–PGR_S relationship was poor in two inbred lines, indicating that kernel set in these two inbred lines was influenced by factors other than PGR_S and DM partitioning. A combination of favorable features of the KN_P–PGR_S relationship of the parental inbred lines was influencing the heterosis for kernel set at all resource levels. Greater stress tolerance under low water availability and high plant density was related to lower PGR_S thresholds for kernel set and high initial response of kernel set with increasing PGR_S. The heterosis for kernel set that was associated with heterosis for EGR_S varied with inbred line–hybrid combination and level of resource availability per plant. Identification of inbred lines with desirable features of the KN_P–PGR_S relationship may aid in the development of hybrids that perform well under optimal and stress conditions.

	ACKNOWLEDGMENTS

 
Technical support by A. Aguilera is gratefully acknowledged.

Received for publication March 9, 2005.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 

• Ahmadzadeh, A., E.A. Lee, and M. Tollenaar. 2004. Heterosis for leaf CO₂ exchange rate during the grain-filling period in maize. Crop Sci. 44:2095–2100.[Abstract/Free Full Text]
• Aluko, G.K., and K.S. Fischer. 1988. The effects of changes of assimilate supply around flowering on grain sink and yield of maize (Zea mays) cultivars of tropical and temperate adaptation. Aust. J. Agric. Res. 39:153–161.
• Andrade, F.H., A. Cirilo, and L. Echarte. 2000. Kernel number determination in maize. p. 59–74. In M.E. Otegui and G.A. Slafer (ed.) Physiological bases for maize improvement. The Harworth Press, Binghampton, NY.
• Andrade, F.H., L. Echarte, R. Rizzalli, A.I. Della Maggiora, and M. Casanovas. 2002. Kernel number prediction under nitrogen or water stress. Crop Sci. 42:1173–1179.[Abstract/Free Full Text]
• Andrade, F.H., C. Vega, S. Uhart, A. Cirilo, M. Cantarero, and O. Valentinuz. 1999. Kernel number determination in maize. Crop Sci. 39:453–459.[Abstract/Free Full Text]
• Bänziger, M., G.O. Edmeades, and H.R. Lafitte. 2002. Physiological mechanisms contributing to the increased N stress tolerance of tropical maize selected for drought tolerance. Field Crops Res. 75:223–233.[CrossRef]
• Cirilo, A.G., and F.H. Andrade. 1996. Sowing date and kernel weight in maize. Crop Sci. 36:325–331.[Abstract/Free Full Text]
• Djisbar, A., and F.P. Gardner. 1989. Heterosis for embryo size and source and sink components of maize. Crop Sci. 29:985–992.[Abstract/Free Full Text]
• Dudley, J.W., M.A. Saghai Maroof, and G.K. Rufener. 1992. Molecular marker information and selection of parents in corn breeding programs. Crop Sci. 32:301–304.
• Echarte, L., F.H. Andrade, C.R.C. Vega, and M. Tollenaar. 2004. Kernel number determination in Argentinean maize hybrids released between 1965 and 1993. Crop Sci. 44:1654–1661.[Abstract/Free Full Text]
• Echarte, L., S. Luque, F.H. Andrade, V.O. Sadras, A. Cirilo, M.E. Otegui, and C.R.C. Vega. 2000. Response of maize kernel number to plant density in Argentinean hybrids released between 1965 and 1995. Field Crops Res. 68:1–8.
• Edmeades, G.O., J. Bolaños, M. Hernández, and S. Bello. 1993. Causes for silk delay in a lowland tropical maize populations. Crop Sci. 33:1029–1035.[Abstract/Free Full Text]
• Fischer, K.S., and A.F.E. Palmer. 1984. Tropical maize. p. 213–248. In P.R. Goldsworthy, and N.M. Fischer (ed.) The physiology of tropical fields crops. J. Wiley & Sons, Bath, England.
• Gama, E.E.G., and A.R. Hallauer. 1977. Relation between inbred and hybrid traits in maize. Crop Sci. 17:703–706.[Abstract/Free Full Text]
• Hallauer, A.R., W.A. Russell, and K.R. Lamkey. 1988. Corn breeding. p. 463–564. In G.F. Sprague and J.W. Dudley (ed.) Corn and corn improvement. Agron. Monogr. 18. 3rd ed. ASA, CSSA, and SSSA, Madison, WI.
• Jandel Scientific. 1991. Table curve v. 3.0. User's manual v. 3.0 AISN software. Jandel Scientific, Corte Madera, CA.
• Leng, E.R. 1954. Effect of heterosis on the major components of grain yield in corn. Agron. J. 46:502–506.[Free Full Text]
• Ritchie, S.W., and J.J. Hanway. 1982. How a corn plant develops. Spec. Rep. 48. Rev. ed. Iowa State Univ. of Science and Technology, Coop. Ext. Serv., Ames.
• Ritchie, J.T., and D.S. NeSmith. 1991. Temperature and crop development. p. 5–29. In R.J. Hanks and J.T. Ritchie (ed.) Modeling plant and soil systems. Agron. Monogr. 31. ASA, CSSA, and SSSA, Madison, WI.
• Samanci, B. 1996. Phenotypic correlations between maize inbreds and their single cross hybrids in short season areas. Euphytica 89:291–296.
• SAS Institute. 1999. SAS statistical package for Windows. v. 8.02. SAS Inst., Cary, NC.
• Shieh, G.J., and F.S. Thseng. 2002. Genetic diversity of Tainan-white maize inbred lines and prediction of single cross hybrid performance using RAPD markers. Euphytica 124:307–313.[CrossRef]
• Shull, G.H. 1908. The composition of a field of maize. Am. Breed. Assoc. Rep. 4:296–301.
• Sinha, S.K., and R. Khanna. 1975. Physiological, biochemical, and genetic basis of heterosis. Adv. Agron. 27:123–174.
• Tokatlidis, I.S. 2000. Variation within maize lines and hybrids in the absence of competition and relation between hybrid potential yield per plant with line traits. J. Agric. Sci. (Cambridge) 134:391–398.[CrossRef]
• Tollenaar, M. 1989. Response of dry matter accumulation in maize to temperature. I. Dry matter partitioning. Crop Sci. 29:1239–1246.[Abstract/Free Full Text]
• Tollenaar, M., A. Ahmadzadeh, and E.A. Lee. 2004. Physiological basis of heterosis for grain yield in maize. Crop Sci. 44:2086–2094.[Abstract/Free Full Text]
• Tollenaar, M., and T.B. Daynard. 1978. Relationship between assimilate source and reproductive sink in maize grown in a short season environment. Agron. J. 70:219–223.[Abstract/Free Full Text]
• Tollenaar, M., L.M. Dwyer, and D.W. Stewart. 1992. Ear and kernel formation in maize hybrids representing three decades of grain yield improvement in Ontario. Crop Sci. 32:432–438.[Abstract/Free Full Text]
• Tollenaar, M., and W. Migus. 1984. Dry matter accumulation of maize grown hydroponically under controlled-environment and field conditions. Can. J. Plant Sci. 64:475–485.
• Tollenaar, M., and J. Wu. 1999. Yield improvement in temperate maize is attributable to greater stress tolerance. Crop Sci. 39:1597–1604.[Abstract/Free Full Text]
• Vega, C.R.C., F.H. Andrade F.H., and V.O. Sadras. 2001. Reproductive partitioning and seed set efficiency in soybean, sunflower and maize. Field Crops Res. 72:163–175.[CrossRef]

This article has been cited by other articles:

				L. Echarte, S. Rothstein, and M. Tollenaar The Response of Leaf Photosynthesis and Dry Matter Accumulation to Nitrogen Supply in an Older and a Newer Maize Hybrid Crop Sci., March 19, 2008; 48(2): 656 - 665. [Abstract] [Full Text] [PDF]

				E. A. Lee and M. Tollenaar Physiological Basis of Successful Breeding Strategies for Maize Grain Yield Crop Sci., December 18, 2007; 47(Supplement_3): S-202 - S-215. [Abstract] [Full Text] [PDF]

				M. Tollenaar, W. Deen, L. Echarte, and W. Liu Effect of Crowding Stress on Dry Matter Accumulation and Harvest Index in Maize Agron. J., June 5, 2006; 98(4): 930 - 937. [Abstract] [Full Text] [PDF]

This Article Abstract Figures Only Full Text (PDF) Free Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (6) Citing Articles via Google Scholar Google Scholar Articles by Echarte, L. Articles by Tollenaar, M. Search for Related Content PubMed Articles by Echarte, L. Articles by Tollenaar, M. Agricola Articles by Echarte, L. Articles by Tollenaar, M. Related Collections Crop Physiology & Metabolism Maize