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Crop Science 42:1894-1901 (2002)
© 2002 Crop Science Society of America

CROP BREEDING, GENETICS & CYTOLOGY

Aflatoxin Accumulation of White and Yellow Maize Inbreds in Diallel Crosses

F. J. Betrán*,a, T. Isakeitb and G. Odvodyc

a Corn Breeding and Genetics Program, Texas A&M Univ., College Station, TX 77845
b Texas A&M Univ., College Station
c Texas A&M Research & Extension Center, Corpus Christi, TX

* Corresponding author (javier-betran{at}tamu.edu)


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
Preharvest aflatoxin (AF) contamination is one of the main limitations for corn (Zea mays L.) production in the southern USA causing enormous economic losses and posing a risk to animal and human health. The objectives of this study were (i) to evaluate and compare hybrids of new and selected potential sources of AF resistance for AF accumulation under field conditions, (ii) to identify the inbreds with the most consistent expression of resistance under different hybrid combinations and growing conditions; and (iii) to estimate combining abilities of white and yellow inbreds for aflatoxin accumulation and secondary traits. Two diallels among six local and exotic white and six yellow maize inbreds were evaluated at three locations in Texas. Inoculation with Aspergillus flavus Link:Fr. isolate NRRL 3357, either directly through the silk channel or as infested kernels on the soil surface, was effective in promoting AF accumulation in hybrids. White hybrids with low aflatoxin were CML269 x TxX24 and CML269 x CML176. CML269, CML176, and CML322 were the white inbreds with the lowest most consistent AF in hybrids and had the best GCA for aflatoxin resistance. Yellow hybrids with low AF were FR2128 x Mp715, Tx772 x Mp715, and Tx772 x CML326. Tx772 and FR2128 had the best GCA for reduced AF across locations or at specific locations. Inbreds CML326 and Tx772 had consistently low aflatoxin accumulation in hybrids across environments. AF content was correlated with husk cover, ear rot ratings, and insect damage. Exotic inbreds have genetic factors that can contribute to the reduction of aflatoxin contamination.

Abbreviations: GCA, general combining ability • SCA, specific combining ability • AF, aflatoxin • CML, CIMMYT maize line • WE, Weslaco, TX • CC, Corpus Christi, TX • CS, College Station, TX


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
AFLATOXIN is a potent toxin and carcinogen produced by the fungus Aspergillus flavus that can cause aflatoxicosis and liver cancer in animals and humans (Castegnaro and McGregor, 1998). Aflatoxin limits corn marketability, causing economic losses because of risk to animal and human health. Preharvest aflatoxin contamination of corn grain is a chronic problem for growers in the southeastern USA (Widstrom, 1996). It is less common in the Corn Belt of the U.S. Midwest but it can be a serious problem in seasons with above average temperatures and drought conditions (Payne, 1992). In 1998, aflatoxin resulted in $85 to $100 million in losses to corn producers in Texas, Louisiana, and Mississippi. The combined crop loss due to aflatoxin epidemics in the southern USA during 1988, 1989, 1990, 1995, 1996, and 1998 surpassed $1000 million. Aspergillus flavus is the predominant producer of aflatoxins B1 (AFB1) and B2 (AFB2). Aspergillus flavus has been known as a pathogen of corn in Texas since 1920 (Taubenhaus, 1920). In the USA, grain with more than 20 ng g-1 of aflatoxin B1 is banned from interstate commerce and that with more than 300 ng g-1 cannot be used as livestock feed.

Aflatoxin contamination has been associated with abiotic stresses such as drought and high temperature (Payne, 1992) and biotic stress such as insect damage (McMillian et al., 1985; Windham et al., 1999). There are different complementary approaches to prevent or reduce aflatoxin: cultural practices to optimize crop production, natural host plant resistance and beneficial secondary traits, biotechnology approaches, and the use of nontoxigenic strains of the A. flavus as biocompetitive agents (Brown et al., 1998; Widstrom, 1987). Biotechnology approaches aim to incorporate resistance through the addition or enhancement of genes that regulate compounds that inhibit aflatoxin production or fungal development and the reduction of aflatoxin production by targeting the gene cluster regulating aflatoxin biosynthesis. Beneficial secondary traits such as husk covering and tightness, physical properties of the pericarp (thickness, wax), and drought or heat stress tolerance are contributing factors to aflatoxin resistance. Hybrids more adapted to the growing area with good husk coverage and insect resistance generally accumulate less aflatoxin (Lillehoj et al., 1975). Resistance to aflatoxin contamination is under genetic control and genetic variation for response to AF has been found in corn (Widstrom et al., 1987; Scott and Zummo, 1988; Campbell and White, 1995a). Sources of natural resistance such as inbreds Mp420, Mp313E, Mp715, Tex6, LB31, CI2, and population GT-MAS:gk have been identified and developed (Scott and Zummo, 1992; McMillian et al. 1993; Campbell and White, 1995a). However, the majority of these sources of resistance lack acceptable agronomic performance and adaptation that preclude their direct use in commercial hybrids. Current efforts are to map and characterize the genetic factors involved in the resistance and to transfer them through marker-assisted selection to more suitable elite material (Rocheford and White, 2000). At present, there are no elite inbreds resistant to aflatoxin that can be used directly in commercial hybrids. The limiting factors in breeding for aflatoxin resistance are the spatial and temporal variation in aflatoxin accumulation that requires inoculation and a high number of replications, the lack of a reliable and inexpensive screening methodology, and the low metabolic activity of corn plants after physiological maturity (Payne, 1992).

Information about the comparative performance and the efficiency of known and potential sources of aflatoxin resistance and of commercial material under field conditions in the south plains of the USA is limited. During 1999, aflatoxin-resistant candidate inbreds and hybrids were evaluated by artificial inoculation in three Texas locations. The material under evaluation had different backgrounds: sources of aflatoxin resistance, subtropical and tropical germplasm with good husk cover and grain quality, and temperate germplasm with good yields and loose husks (Betrán et al., 2000). Inbreds such as CML269, CML322, CML176, Tex6, and Mp313E among the whites, and Tx772 and FR2128 among the yellows showed promising results. The objectives of this study were (i) to evaluate and compare hybrids of new and selected potential sources of aflatoxin resistance for aflatoxin accumulation under field conditions, (ii) to identify the inbreds with the most consistent expression of resistance under different hybrid combinations and growing conditions, and (iii) to estimate combining abilities of white and yellow inbreds for aflatoxin accumulation and secondary traits.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Germplasm
On the basis of 1999 data (Betrán et al., 2000), two diallels among the most resistant yellow and white inbreds were evaluated at three locations in South and Central Texas: College Station (CS), Weslaco (WE), Corpus Christi (CC) during year 2000. The inbreds varied in adaptation from temperate to tropical environments (Table 1) . Single crosses without reciprocals were produced in our winter nursery at Homestead, FL, during 1999. In addition to the 15 single crosses involved in the diallel, five check hybrids at CS and WE, and six at CC were evaluated in the same experiment. The checks were commercial hybrids with different response to aflatoxin in previous evaluations (Cargill7997 and P31B13 as susceptible checks, and P30R39 and DKXL269 as resistant checks), and hybrids of resistant inbreds Tex6 among the white hybrids and Mp715 among the yellow hybrids.


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  		Table 1. White and yellow maize inbreds evaluated in two diallels for aflatoxin contamination in three southern USA locations during summer 2000.

 
Corn Inoculation and Aflatoxin Quantification
Aspergillus flavus isolate NRRL3357 was used in the study. At CS and WE, 20 plants per plot were inoculated with a conidial suspension containing 3 x 107 conidia of A. flavus in 3 mL distilled water injected 6 to 10 d after midsilk by the nonwounding silk channel inoculation technique (Zummo and Scott, 1989). At CC, inoculation was done by placing A. flavus colonized corn kernels on the soil surface between treatment rows when the first hybrids reached mid-silk stage. The inoculum was distributed at the rate of 1 kg (noncolonized dry seed equivalent) per 200 foot of row. Inoculated ears at CS and WE, and all the ears in the plot at CC were hand harvested after kernel moisture in all hybrids was below 150 g kg -1. Ears were husked, rated for insect injury and visible fungi colonization, dried, and shelled. The kernels were bulked within plots. At CC, threshed grain from the nine replicates of each hybrid were pooled into three composite replicates as follows: Reps (1,2,3), (4,5,6), and (7,8,9). This procedure was used to reduce the effect of spatial variation within the trial without increasing the number of grain samples to analyze for aflatoxin. The whole kernel samples were ground with a Romer mill (Union, MO). Quantification of aflatoxin was conducted in 50-g subsamples from each plot with monoclonal antibody affinity columns and fluorescence determination by the Vicam Aflatest (Watertown, MA). Aflatoxin content was expressed in nanograms per gram (ppb). At CS and WE, noninoculated ears from several plots in each experiment were also harvested and similarly analyzed to estimate the efficiency of the inoculation process by comparing the aflatoxin accumulation of inoculated vs. noninoculated ears in the same plot.

Field Management Measurements
Alpha-lattice field experimental design with four replications at CS and WE, and 9 replications at CC was used (Patterson and Williams, 1976). Plots at CS and WE were 6.4 m long and 0.75 m apart, and 7.90 m long and 0.96 m apart at CC. No insecticides were applied after planting. Trials were planted at regular times in WE (middle of February) and CS (early March). Drought and heat stress was induced by late planting at CC (4 weeks later than usual planting time, which is the middle of February), and by limited irrigation at WE and CS. In addition to aflatoxin content, the following secondary traits were measured: male flowering (MF) and female flowering (FF) as days from planting to anthesis or silking, respectively, anthesis silking interval (ASI) as the difference in days between FF and MF (ASI = FF - MF), visual rating for the number of ears with presence of A. flavus (1, no visual presence to 5, most of the ears with the fungus present), visual ratings for the number of ears with insect damage (1, no visual damage to 5, most of the ears with insect damage), visual rating for husk cover from 1 (good: tight long husks extending beyond the tip of the ear) to 5 (poor: loose short husks with exposed ear tips), grain texture as visual rating from 1 (flint: round crown kernel and vitreous appearance) to 5 (dent: kernels with dentation and floury endosperm). At CC adjusted grain yield per plot in grams per plot and insect injury ratings dependent on the length of the insect galleries on the ear were recorded (Widstrom, 1967).

Statistical Analysis
Aflatoxin contents in nanograms per gram were transformed to log (ng g-1) to equalize variance. Antilogarithmic values were used to report the results. Individual analyses of variance were conducted for each trial and stress level with the PROC MIXED procedure form SAS (SAS, 1997). Genotypes (hybrids or inbreds) were considered fixed effects. The adjusted means, if the incomplete block design was more effective than randomized complete block design (RCBD), or unadjusted means, if RCBD was more effective, were used to estimate GCA and SCA effects. Combined analyses of variance were conducted with the SAS GLM procedure (SAS, 1997). Griffing Method IV Diallel analysis was used to estimate GCA for the lines and SCA for the hybrids in all environments (Griffing, 1956).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Aflatoxin Accumulation
Significant differences among the hybrids means, their SCA effects, and among inbred GCAs were detected at all three locations except at CS for the white inbred GCAs and hybrid SCAs. Genotype x environmental (GxE), GCAxE and SCAxE interactions for aflatoxin content were significant for both yellow and white hybrids. Therefore, the results reported here are by individual environments. Other studies have demonstrated a great influence of the environment in screening for aflatoxin response (Payne, 1992).

The levels of aflatoxin contamination were greater at WE and CC than at CS. For the white hybrids, the average aflatoxin content was 383.0 ng g-1 at WE ranging from 44.3 to 1235 ng g-1, 195.3 ng g-1 at CC ranging from 23.3 to 1233.3 ng g-1, and 89.4 ng g-1 at CS ranging from 15.5 to 382.8 ng g-1 (Table 2) . For the yellow hybrids, the average aflatoxin content was 408.3 ng g-1 at WE ranging from 17.7 to 2147.5 ng g-1, 472.1 ng g-1 at CC ranging from 106.7 to 1060.0 ng g-1, and 110.3 ng g-1 at CS ranging from 21.9 to 789.8 ng g-1 (Table 3) . These levels of aflatoxin contamination are relatively high compared with other studies (Widstrom et al., 1984; Scott and Zummo, 1988). The silk channel inoculation technique was effective as indicated by the comparison between inoculated and noninoculated ears harvested in the same plots both at WE (703 ng g-1 vs. 37 ng g-1) and CS (67.14 ng g-1 vs. 2 ng g-1) (Fig. 1) . Even at CS, which had lower AF content overall, the differences between inoculated and noninoculated samples were significant. Environmental conditions that included drought stress and hot temperatures after flowering were favorable for aflatoxin production at WE and CC.


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  		Table 2. Aflatoxin accumulations (AF) and rank (parentheses), and specific combining ability effects (SCA) of white maize hybrids for aflatoxin contamination in three southern USA locations during summer 2000.

 

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  		Table 3. Aflatoxin accumulation (AF) and rank (parentheses), and specific combining ability effects (SCA) of yellow maize hybrids for aflatoxin accumulation in three southern USA locations during summer 2000.

 


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  		Fig. 1. Aflatoxin content (ng g-1) for inoculated ears with the silk channel inoculation technique (left bars) and noninoculated ears (right bars) in white and yellow hybrids in two environments.

 
At CC, the new A. flavus-colonized kernel technique (Odvody, 2000) to increase the amount of inoculum available for natural infection proved to be effective for aflatoxin production and hybrid classification. At CS, where the plants were damaged by hail, several summer storms minimized drought stress. Yellow and white hybrids were in different but adjacent experiments in all three locations. Although our experimental design does not permit statistical comparison of individual yellow and white hybrids, on average yellow hybrids were more susceptible to aflatoxin contamination than white hybrids at all the locations, but especially at CC where yellow hybrids had an average content of 472.1 ng g-1 while white hybrids had 195.3 ng g-1. This difference in response to aflatoxin of white and yellow hybrids is due to germplasm differences and it should not be associated with the trait of grain color itself. White corn normally used for food purposes has been strongly selected for kernels with a high proportion of flinty endosperm, intact kernels free of insect damage, fissures, and stress cracks, which are traits associated with less aflatoxin.

Aflatoxin in F1 Hybrids and Combining Abilities of White and Yellow Inbreds
The white hybrids with less aflatoxin were CML269 x TxX24 (44.3 ng g-1) and CML269 x CML176 (45.8 ng g-1) at WE, CML269 x CML176 (23.3 ng g-1) and resistant check CML176 x Tex6 (33.3 ng g-1) at CC, and CML343 x Tx114 (15.5 ng g-1) and CML384 x Tx114 (19.0 ng g-1) at CS (Table 2). The white hybrids with consistently low aflatoxin accumulation across environments were CML269 x TxX24, CML322 x CML176 and CML269 x CML176 (Table 2). The inbreds with the lowest average for aflatoxin accumulation across hybrids were CML269 (179.70 ng g-1) at WE, CML176 (52.00 ng g-1) at CC, and CML322 (56.05 ng g-1) at CS (Table 4) . The inbreds with the best GCA for aflatoxin were CML269 (-240.33 ng g-1) and CML322 (-121.58 ng g-1) at WE, and CML176 (-61.67 ng g-1) and CML322 (-21.65 ng g-1) at CC (Table 4). GCA effects were not significant at CS. The white inbreds that showed the least aflatoxin have subtropical or tropical origin (Table 1). Inbreds more adapted to temperate environments had higher aflatoxin contents than subtropical inbreds. The differences in maturity between early-flowering temperate inbreds and subtropical/tropical inbreds could play a role in the response observed in their hybrids. However, the inoculation took place approximately at the same reproductive stage and during more favorable conditions for aflatoxin production (i.e., warmer temperatures and less rainfall) occurred later in the season in all three environments. Therefore, it appears that the subtropical and tropical white inbreds carry underlying genetic factors that reduce the susceptibility of their hybrids to aflatoxin. Some of the resistant inbred Tex6 hybrids used as checks were also low in aflatoxin contamination at all three locations (Table 2). Inbred Tex6 was selfed from Whitemaster (PI401763), a southern corn variety from Texas (Campbell and White, 1995a). The inbred was difficult to increase and maintain under Texas conditions but its hybrids performed well under A. flavus inoculation.


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  		Table 4. Average means across hybrid combinations and general combining ability effects (GCA) of white maize inbreds for aflatoxin contamination in three southern USA locations during summer 2000.

 
The yellow hybrids with less aflatoxin were resistant check Tx772 x Mp715 (17.8 ng g-1) and Tx772 x CML326 (125.8 ng g-1) at WE, commercial check DKXL269 (106.7 ng g-1) and FR2128 x Mp715 (150 ng g-1) at CC, and TX772 x Mp715 (22 ng g-1), and Tx772 x CML326 (24.5 ng g-1) at CS (Table 3). The yellow hybrids Tx772 x CML326 and Tx772 x Mp715 were the most consistent for low aflatoxin accumulation across environments. The inbreds with the lowest aflatoxin average across hybrid combinations were Tx772 (167.4 ng g-1) at WE, CML326 (352.0 ng g-1) at CC, and Tx772 (38.8 ng g-1) at CS (Table 5) . The inbreds with the best GCA for aflatoxin resistance were Tx772 and CML285 at WE, CML326 and FR2128 at CC, and Tx772 at CS (Table 5). Checks with parental inbred Mp715, an aflatoxin resistant inbred from Mississippi, had low aflatoxin. The southern inbreds, Mp420 from Mississippi (Scott and Zummo, 1992) and Tx601y from Texas, which are considered adapted to the testing area and resistant to aflatoxin, had significant positive GCA effects. The temperate yellow inbreds Tx772 and FR2128 had lower aflatoxin than subtropical inbreds. Both of these lines have vitreous endosperm and good kernel integrity at harvest. Tx772 is a temperate inbred with flint and orange grain color developed from Argentine germplasm (Table 1). Important differences (e.g., GCA x environment interactions) in the average response of parental inbreds to aflatoxin in hybrids were significant between the WE and CC locations (Table 5). Tx772 had negative GCA at WE and CS but it had positive GCA at CC. Likewise FR2128 had positive GCA at WE and negative GCA at CC. Response of hybrids to aflatoxin depends on several factors such as differences in planting date, environmental conditions, cultural practices, harvest date and insect injury (Payne, 1992). Corpus Christi suffered greater insect pressure than did WE and CS and Tx772 was susceptible and had positive GCA for ear insect injuries. Although the different inoculation method used at CC could have an effect in these differences, similar changes in response of hybrids between CC and WE and CS were observed in previous evaluations where the same inoculation method was used in all three locations (Betrán et al., 2000). Campbell and White (1995b) found hybrids with different response to AF between midwestern and southern locations.


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  		Table 5. Average means across hybrid combinations and general combining ability effects (GCA) of yellow maize inbreds for aflatoxin contamination in three southern USA locations during summer 2000.

 
The development and identification of inbreds resistant to preharvest aflatoxin contamination is strongly influenced by the environment with high variation within and among locations and years (Payne, 1992). Despite these limitations consistent heritable differences among hybrids have been reported (Scott et al., 1991). In our study, hybrids of the most resistant inbreds (CML269, CML322, Tx772) had low aflatoxin accumulation, similar to that found in hybrid trials conducted across several locations in the southern USA (Williams et al., 2000). Exotic inbreds with subtropical and tropical origin adapted to the environmental growing conditions of the South have genetic factors that contribute to reduction of aflatoxin contamination.

The genetic interpretation of diallels with reduced number of parental inbreds such as the ones in this study can be biased by the lack of independent distribution of genes in the parental lines (Baker, 1978). Therefore, combining abilities reported here could be biased by the correlation of gene frequencies and should be interpreted with caution. Despite this limitation, diallel analysis involving the most promising sources of resistance facilitates the identification of parental inbreds with the most consistent response in different hybrid combinations and environments. The genetic information from this study is useful to identify the best sources of aflatoxin resistance for southern areas that can be used in genetic studies to identify loci involved in the resistance or in breeding programs as donors of resistance. Inbreds CML269, CML322, CML176, Tx772, and CML326 are good candidates for identification of quantitative trait loci (QTL) associated with aflatoxin and subsequent introgression into commercial lines.

A practical use of diallel analysis is to estimate the relative importance of general and specific combining ability in determining hybrid performance (Baker, 1978). The most prevalent type of gene action was variable and inconsistent across environments (data not shown). Additive effects were more important for yellow hybrids at WE and for white hybrids at CC. Nonadditive effects were more important for yellow hybrids at CC and for white hybrids at WE. Studies on the inheritance of aflatoxin resistance using diallel mating designs have shown that additive effects are more important than dominance effects in general (Zuber et al., 1978, Widstrom et al., 1984). However, the results have been variable depending on the testing environment, method of inoculation, and sampling procedure. Using the same parental inbreds, Gardner et al. (1987) reported that nonadditive effects (e.g., SCA) were prevalent for resistance while both Zuber et al. (1978) and Darrah et al. (1987a) found GCA accounted for most of the genetic variation. Widstrom et al. (1984) did not detect significant SCA effects in two diallels of sweet corn and yellow dent corn when combined over years but they found significant SCA effects within years. Similar to the CS environment GCA effects were nonsignificant when the incidence of aflatoxin contamination was low (Widstrom et al, 1984). Campbell and White (1995a) reported that both additive and dominant gene action were important for resistance to Aspergillus ear rot when generation mean analysis was used in several maize crosses. The relative importance of each one depended on the cross considered.

Secondary Traits and Aflatoxin Contents
Aflatoxin was correlated with other traits in both white (Table 6) and yellow hybrids (Table 7) . Aflatoxin of white hybrids was positively correlated with texture ratings at CS (0.53**) and CC (0.62**), with ear rot at CS (0.48*), and with insect ratings (0.79**) and ear injury (0.79**) at CC (Table 6). Aflatoxin of yellow hybrids was positively correlated with ear rot ratings (0.84**) and husk cover ratings (0.44*) at CS, with husk cover ratings (0.49*) at WE, and with insect damage ratings (0.66**) and ear injury (0.55**) at CC. At CC, large populations of naturally occurring corn earworm [Heliothis zea (Boddie)] and fall armyworm [Spodoptera frugiperda (J.E. Smith)] caused significant ear injuries. Both husk cover and insect resistance are contributing secondary traits to aflatoxin resistance (Brown et al., 1998, Widstrom, 1987). Payne (1992) described how insects can transport and disseminate the inoculum into the ear and predispose the plant to infection by injuring the pericarp. Campbell and White (1995b) also found a positive correlation between Aspergillus ear rot ratings and aflatoxin production. Flint white and yellow hybrids were less susceptible to aflatoxin than dent hybrids. When Darrah et al. (1987b) evaluated 12 CIMMYT germplasm pools and 17 advanced populations at 10 locations in the USA and Mexico, they found that dent endosperm types had more aflatoxin. Aspergillus flavus colonized the kernel surfaces and infected the kernels after kernel integrity was lost. Hybrids with more vitreous endosperm had better visual kernel integrity than dent hybrids. Although the correlation between maturity measured as silking date and aflatoxin was not significant, in general, early maturing hybrids had higher aflatoxin content than late maturing hybrids (data not shown). Lillehoj et al. (1983) reported that short season hybrids were more likely to have higher aflatoxin than full season hybrids in the Southeast. ASI is a secondary trait indicative of drought susceptibility (Bolaños and Edmeades, 1996). Hybrids with high ASI values showing lack of synchrony between pollen shedding and silking had higher aflatoxin accumulation.


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  		Table 6. General combining effects (GCA) of white maize inbreds for secondary traits and their correlation with aflatoxin (AF) accumulation using hybrid means in three southern USA locations during summer 2000.

 

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  		Table 7. General combining ability effects (GCA) of yellow maize inbreds for secondary traits and their correlation with aflatoxin (AF) accumulation using hybrids means in three southern USA locations during summer 2000.

 
The most AF resistant white inbreds in this study, CML269 and CML322, had good GCA values for insect damage, ear rot, and grain yield (Table 6). This indicates that aflatoxin resistance and agronomic performance can be combined in single genotypes and makes these inbreds excellent candidates for additional breeding efforts. Yellow inbreds FR2128 and CML285 had the best GCA for insect damage (Table 7). FR2128 and CML326 showed the best GCA for grain yield at CC. Tx601 had the best GCA for husk cover. For both yellow and white hybrids grain yield and aflatoxin contents were not correlated at CC.

The characterization of the expression of beneficial secondary traits associated with aflatoxin resistance (e.g., husk cover, insect resistance) in hybrids from promising parental inbreds enable identification of the most suitable donors for improvement of these traits. Breeding towards the pyramiding of different beneficial traits or the introgression into elite genotypes can reduce the risk of aflatoxin contamination. For example, a genotype with the agronomic performance and yield potential of FR2128, the husk cover and grain quality of Tx601, and the low insect damage of CML269 together would have a good combination of traits to minimize aflatoxin.


   ACKNOWLEDGMENTS
 
We thank Frank Fojt III, Dennis Transue, Sandeep Bhatnagar, Cindy King, Jeff Remmers, Carlos Gonzalez, Charles Chilcutt, Beto Garza, John Drawe, Marvin Miller, Rick Hernandez, Joe Rivera, and Eugene Jimenez for their assistance conducting the field trials, processing the plot samples, conducting insect injury ratings and analyzing aflatoxin content. This research was partly funded by an USDA aflatoxin competitive grant and the Texas Corn Producers Board.

Received for publication December 10, 2001.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 




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