| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
a HortResearch, Private Bag 3123, Hamilton, New Zealand
b Plant Breeding Genetics & Biochemistry Division, International Rice Research Institute, DAPO Box 7777, Metro Manila, Philippines
* Corresponding author (esacks{at}hortresearch.co.nz)
 |
ABSTRACT |
|---|
 TOPNOTES ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
INTRODUCTION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Though cultivars of Asian (O. sativa) rice vary in ratooning ability when grown in paddies, the species is only weakly perennial, especially under upland conditions. Thus, genes from strongly perennial wild relatives of O. sativa will be needed to realize our goal of developing a perennial cultivar for the uplands.
Oryza longistaminata (2n = 24, AA) is a potentially useful source of genes for developing perennial upland rice. Oryza longistaminata is a highly diverse, allogamous species that is broadly distributed throughout Africa. Typically, accessions of O. longistaminata are strongly perennial and have vigorous rhizomes. However, natural populations of O. longistaminata mostly grow in standing water, so they may lack adaptation to upland conditions. Oryza sativa and O. longistaminata are considerably diverged as compared with other AA species (Aggarwal et al., 1999). To obtain F1 interspecific progeny and the first few backcross generations, in vitro embryo rescue is usually required.
The main objective of this study was to assess the potential of O. longistaminata as a donor of perennial growth traits for upland rice by evaluating interspecific progeny in nonpuddled field conditions. In addition, we compared survival in an area of a field that received infrequent irrigation during the dry season, with survival at in a nearby area that received frequent irrigation. We also investigated the effect of postharvest cutting height on survival.
|
MATERIALS AND METHODS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Oryza sativa cultivars were chosen primarily for adaptation to upland production. With the exception of UPL-Ri-5, which was included as a high-yielding check, the cultivars evaluated were parents in the intermated population. All cultivars used in this study can be obtained from IRRI's Genetic Resources Center (http://www.irri.cgiar.org/GRC/GRChome/home.htm; verified 30 July 2002).
Trials
Two entry x irrigation area trials and one postharvest cutting height trial were conducted. To comply with Philippine plant quarantine regulations, the O. longistaminata parental genotypes were not included in field trials. Seeds for all trials were sown in flats on 29 July 1999 and grown in a glasshouse. Seedlings were transplanted to the field on 14 or 16 Aug. 1999. Plots were 3 m long. Rows were spaced 30 cm apart and within each row, plants were spaced 25 cm apart, for a total of 12 seedlings. The trials were planted on a gently sloping upland field at IRRI's headquarters (14°11' N, 121°15' E), Los Baños, Laguna Province, Philippines. Drainage trenches were dug to carry water off the field. The field soil was a silty clay-loam with a pH of 5.9 ± 0.2. Fertilizer (15 kg ha-1 of N, P, and K) was applied at planting (wet season, July 1999), and on 4 Feb., 30 March, 16 June, and 22 Aug. 2000.
The irrigation areas were opposite sides of a 1-ha field. During the dry season (January through May), the field was separated into a wet side and a dry side by an 18-m-wide strip of nonirrigated land. The wet side was sprinkler irrigated for approximately 5 h once per week. The soil on the dry side was saturated by 7 to 16 h of sprinkler irrigation over 1 to 2 d starting on 29 Feb., 30 March, and 2 May 2000. During the rainy season (June through December), supplemental irrigation was not needed. Thus, the main difference between irrigation areas was availability of water during the dry season.
Entry x Irrigation Area Trials
The two entry x irrigation area trials were 
lattice (0,1) designs with two irrigation areas, two or three replications per irrigation area (depending on the trial), and 10 blocks per replication. Plots were single rows. The trial with two replications compared 14 check cultivars and 51 S1 families. The trial with three replications compared 16 check cultivars and 54 S1 families. Sixteen S1 families were common to both trials. Availability of seed determined the trial in which the entries were used. Upon harvesting, plants were cut 25 to 30 cm above the ground and allowed to regrow.
Cutting Height Trial
We investigated the effect of cutting height at harvest on postharvest survival. The cutting height trial was a split plot design, with three postharvest cutting treatments assigned to whole plots, and 14 entries assigned to subplots. There were three replications of whole plots. Subplots were 2 rows containing 24 plants. All plots in the cutting height trial were on the dry side of the field. Cutting treatments were high = stems uncut with only panicles removed, medium = stems cut half way between the soil surface and the flag leaf, and low = stems cut 15 cm above the soil surface. Plants were cut in December 1999 after the initial harvest and again in March 2000 after harvest of the ratoon crop. Entries consisted of two cultivars and 10 S1 families. Five S1 families were common to the cutting height trial and the entry x irrigation area trials.
Data Collection
Data on vegetative vigor, survival and presence of rhizomes were recorded. Individual plants in plots were measured. IRRI's 1 to 9 scale for vegetative vigor (IRRI, 1996) was modified to include a value for dead plants: 1 = extra vigorous, 3 = vigorous, 5 = normal, 7 = weak, 9 = very weak, 10 = dead. Initial vigor was recorded in October 1999, before the first harvest. Approximately 1 yr after planting, vigor and survival were recorded on 2 and 3 Aug. 2000 for the entry x irrigation area trials, and on 15 Aug. 2000 for the cutting height trial. For the cutting height trial, vigor and survival also were recorded approximately seven months after planting on 23 March 2000. Presence of rhizomes was recorded for all trials through the first 6 mo after transplanting. Plants that had at the soil surface a distance between consecutive shoots of 3.5 cm or more were scored as rhizomatous.
To avoid loss of seed from shattering and to comply with Philippine plant quarantine regulations, panicles of interspecific progeny were enclosed in nylon net bags (approximately 15 by 30 cm). Panicles of cultivar controls were also enclosed in net bags but some bird damage was observed before bagging was completed. Panicles were harvested when mature.
For entry x irrigation area trials only, data on yield, awning, and threshability were also taken. Harvested seed from each plant was weighed. Plant height was recorded between 11 and 14 Oct. 1999. The lengths of three awns from each plant were measured. Panicle threshability was determined after harvest and drying by means of IRRI's standard, 1 to 9, scale (IRRI, 1996); 1 = difficult (<1% shattering), 9 = easy (51–100% shattering).
Statistical Methods
Analyses of variance were conducted with SAS procedure MIXED, using type III sums of squares (Littell et al., 1996; SAS Institute Inc., 1990). For the entry x irrigation area trials, entry type (cultivar or progeny), entries, and irrigation area (wet or dry side) were considered fixed effects; replications nested in irrigation areas and blocks nested in replications were considered random effects. For the cutting height trial, cutting treatment and entry were considered fixed effects; replications were considered random effects. For all analyses, interactions between fixed and random effects were considered random, degrees of freedom were calculated via the Satterthwaite option, and means were obtained with the lsmeans statement.
Segregation ratios for rhizome expression were evaluated by chi-square tests with SAS procedure FREQ. To determine if there was an association between rhizome presence and 1 yr survival within families that segregated for rhizome production, Fisher's exact tests were performed with SAS procedure FREQ (SAS Institute Inc., 1990).
|
RESULTS AND DISCUSSION |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
|
|
The limited survival observed for O. sativa/O. longistaminata progeny may have resulted from a lack of selection for perenniality while developing the intermated population, a low initial frequency of upland adaptation genes from O. longistaminata, recessive perenniality genes, or a combination of factors. To produce future populations with a high frequency of perennial individuals, it may be worthwhile to select for perenniality early in the populations' development and to choose perennial O. longistaminata parents that are from seasonally dry sites. Nevertheless, the population already produced for this study was considerably more perennial than representative cultivars of upland rice.
Out of 5352 progeny, 37 rhizomatous individuals were identified. None of the cultivars produced rhizomes and only 14 S1 entries produced any individuals with rhizomes. Of the 14 segregating S1 entries, 12 had fewer than 5% rhizomatous individuals (Fig. 1). However, two families, UPR-3033-97-1 and UPR-4499-98-1, produced approximately 25% rhizomatous individuals; each family had 47 individuals.
Grain yield during the wet season was significantly higher for cultivars than for S1s (Table 1), even though birds reduced the harvested yield of cultivars but not S1s. Without bird damage, we would have expected wet season yields of the cultivars to range from approximately 10 to approximately 35 g plant-1. Variation among cultivars and among S1s for wet season yield was significant (Table 1). The low yields of nearly all S1 families (Table 1) are indicative of infertility, which is common in early generations of O. sativa/O. longistaminata crosses (Oka, 1988). Low fertility is a considerable handicap for introgressing complexly inherited traits because the ability to produce recombinants is hampered. Yields during the dry season were near 0 g plant-1 for all entries (Table 1). During the dry season, none of the entries yielded in the dry irrigation area but some yielded in the wet irrigation area, indicating that insufficient water limited plant productivity.
Plant height was, on average, slightly greater for cultivars than for S1 families (Table 1). Variation among cultivars and among S1s for plant height was significant. Most progeny entries had an acceptable height for upland cultivation.
Awning and shattering are undesirable traits that were more common in progeny entries than in cultivars (Table 1). The variation observed among and within S1 families would permit selection for improved type (Table 1). Indeed, even without selection, some S1 families were already fixed for the awnless trait (Table 1).
Cutting Height Trial
When rice is harvested, the plants are typically cut back close to the ground. Theoretically, the amount of starch reserves in roots and remaining shoots after cutting should affect the plant's ability to ratoon. However, studies on how cutting height affects ratooning of irrigated rice have produced inconsistent results (Chauhan et al., 1985).
In this study, survival of the high cutting treatment at 7 mo was significantly greater than that of the medium and low treatments (Table 2). Survival of the medium treatment was slightly greater than that of the low treatment but this difference was not significant (Table 2). These data suggest that leaving as much stubble as possible after harvest would improve a plant's chances of survival. The high cutting treatment is analogous to the natural condition of wild plants. However, leaving cultivated plants uncut is impractical because harvested culms senesce and if left uncut, they cause the whole ratooned plant to lodge. Several studies of irrigated rice have indicated that cutting plants 15 cm above the soil is better than cutting at soil level (Chauhan et al., 1985). In the absence of further information, the best compromise may be to cut just enough to prevent lodging.
|
Rhizome Genetics
The frequency of rhizomatous individuals for three families indicated that a single locus can have a large effect on rhizome presence in the population studied. Though the chi-square test indicated that the ratio of rhizome absence:presence for UPR-2044-97-1 (Table 2) was marginally different from 3:1 (P = 0.045), the homogeneity chi-square for UPR-2044-97-1, UPR-3033-97-1, and UPR-4499-98-1 indicated that pooling was valid (P = 0.352). The pooled chi-square indicated that the data fit a 3:1 ratio (P = 0.120). If we included in the analyses the 16 nonrhizomatous UPR-2044-97-1 individuals from the entry x irrigation area trial (Table 2), the results were essentially the same as above.
Maekawa et al. (1998) studied an O. sativa/O. longistaminata F2 population using different parental genotypes from those used in this study and found that rhizomatous growth habit was governed by a single dominant gene, Rhz, located on chromosome 4. In our population, the use of surface observations alone for identifying rhizomatous genotypes could lead to the conclusion that rhizome presence was recessive because the F1 and many of the subsequent progeny (Fig. 1) appeared to lack rhizomes with this method of detection. However, by removing soil and roots, we observed that our O. sativa/O. longistaminata F1 had rhizomes that were too short (1–3 cm) to discern from the soil surface, and these were shorter than the average of the two parents, suggesting that rhizome expression was partially recessive. Additionally, some pots of the S1 parental individuals, UPR-3033-97-1 and UPR-4499-98-1, produced long rhizomes that were visible by surface observations, indicating that environmental factors also affected rhizome expression. Removing soil and roots confirmed that the parents UPR-2044-97-1, UPR-3033-97-1, and UPR-4499-98-1 were rhizomatous. The different methods used by the two studies (surface observations vs. digging, and upland vs. paddy) and genetic differences between the populations studied may account for the apparent discrepancy in results.
The low frequency of rhizomatous individuals and segregating families in our population suggests that factors in addition to the Rhz gene were involved. Maekawa et al. (1998) noted that the degree of rhizome expression in their population varied and surmised that genes in addition to the Rhz gene influenced the trait. In addition, we have observed large and consistent differences in rhizome expression among three O. sativa/O. longistaminata F1s that were grown side-by-side in a greenhouse but were derived from different parents (data not shown), suggesting that different alleles or allelic combinations can cause differences in rhizome expression among populations. Moreover, rhizomatous individuals were rarely obtained when O. sativa/O. longistaminata F1s were backcrossed to O. sativa (IRRI, 1998; Tao et al., 2003, in press), further supporting the conclusion that loci other than Rhz are involved. It is likely that the presence of different Rhz alleles in the two populations and/or factors in addition to Rhz accounted for some of the differences in phenotype among the population studied here and Maekawa et al.'s (1998) population. Such factors may include the presence of different alleles in the two populations, different epistatic interactions, genotype x environment effects, and segregation distortion.
In contrast to our population, the populations studied by Maekawa et al. (1998) and Tao et al. (2003)(in press) produced rhizomatous progeny with greater frequency. Thus, choice of O. sativa/O. longistaminata population can make a large difference in the frequency of rhizomatous individuals. Because vigorous rhizomatous growth is a common feature of O. longistaminata accessions, the knowledge that variation for rhizome expression among O. sativa/O. longistaminata populations can be large is an important and unexpected finding. To introgress the rhizome trait, the breeder would be wise to identify and choose conducive populations over recalcitrant ones.
The close genetic relationship among grass species makes comparisons of traits across different grasses meaningful (Ahn and Tanksley, 1993; Peng et al., 1999). A commonality of studies on rice, maize (Zea mays L.), and sorghum [Sorghum bicolor (L.) Moench] has been the expression of fewer and shorter rhizomes in the F1, relative to the rhizomatous parent (Camara-Hernandez and Mangelsdorf, 1981; Kulakow and Ennis, 1988; Mangelsdorf et al., 1981; Paterson et al., 1995). Data from F2 populations indicated that rhizome production was inherited in a mostly recessive manner in maize (Camara-Hernandez and Mangelsdorf, 1981; Mangelsdorf et al., 1981) but was dominantly inherited in tetraploid sorghum (Kulakow and Ennis, 1988). In a diploid sorghum population, Paterson et al. (1995) found that rhizomatousness was controlled by eight QTLs distributed on six chromosomes. Rice's relatively small and less duplicated genome could be used to advantage for more fully understanding the genetics of rhizome production in the grasses. Given the difficulties of working with interspecific crosses, efforts should also be made to obtain intraspecific doubled haploid populations by crossing rare O. longistaminata genotypes that lack rhizomes with typical genotypes that are highly rhizomatous, because these would have great potential to elucidate the genetics of rhizome expression. A detailed understanding of rhizome inheritance in the grasses would help researchers devise better strategies for developing perennial crops and for combating invasive weeds.
Survival-Rhizome Association
Most individuals that survived 1 yr lacked rhizomes, indicating that rhizome production is not necessary for perennial growth in materials derived from O. longistaminata. Fisher's exact test based on pooled data from UPR-2044-97-1, UPR-3033-97-1, and UPR-4499-98-1 indicated that 1-yr survival was not associated with rhizome presence (P = 0.091), even though these families segregated for rhizome presence. If the data for each family were analyzed separately, only UPR-4499-98-1 showed a significant positive association between 1-yr survival and rhizome production (P = 0.035). Perhaps rhizome production cannot confer or improve perenniality in the absence of other traits that would give adaptation to upland conditions during the dry season (e.g., drought tolerance). Kulakow and Ennis (1988) found that sorghum needed long, deep rhizomes to survive the cold winter in Kansas, USA., and that short, shallow rhizomes were not sufficient to confer perenniality. Analogously, we might expect that deep rhizomes could help rice avoid drought stress, so rhizome depth may be a useful criterion for choosing parental material.
|
CONCLUSIONS |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
|
ACKNOWLEDGMENTS |
|---|
|
NOTES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
Received for publication August 23, 2001.
|
REFERENCES |
|---|
|
TOPNOTESABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTS AND DISCUSSIONCONCLUSIONSREFERENCES |
|---|
This article has been cited by other articles:
|
|
 |
|
  E. L. PLOSCHUK, G. A. SLAFER, and D. A. RAVETTA Reproductive Allocation of Biomass and Nitrogen in Annual and Perennial Lesquerella Crops Ann. Bot., July 1, 2005; 96(1): 127 - 135. [Abstract] [Full Text] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
| The SCI Journals | Agronomy Journal | Vadose Zone Journal | |||
| Journal of Plant Registrations | Soil Science Society of America Journal | ||||
| Journal of Natural Resources and Life Sciences Education |
Journal of Environmental Quality |
||||
