Effects of selection criteria on yield stability in chickpea (Cicer arietinum L.)

Summary Selection in the F₃ generation for seed yield, fruiting branches/plant, effective pods/plant, and seed index (100-seed weight) was carried out in two chickpea crosses. Sixty F₅ lines (15 lines/selection criterion) along with check variety were evaluated for seed yield in three distinct environments. The effects of selection criteria on yield stability was examined using linear regression approach and genotype-grouping technique. There were no differences between selection criteria for linear yield responses of F₅ lines to different environments. Within all four selection criteria the lines showed similar linear responses. The non-linear component was relatively higher for lines selected for effective pods and seed index than lines selected for yield and fruiting branches. On the basis of mean yield and coefficient of variation across environments, the seed index was the least effective selection criterion for developing high yielding and stable lines. When the results of stability parameters and genotype-grouping technique were considered together, selection for yield and fruiting branches was highly effective for isolating stable and high yielding lines.     

Exploitation of wild Cicer species for yield improvement in chickpea

 Chickpea (Cicer arietinum L.) ranks third in the world, and first in the Mediterranean basin, for production among pulses. Despite its importance as a crop and considerable research effort, traditional breeding methods have so far been unable to produce cultivars with a large impact on chickpea production. Interspecific hybridization is known to improve yield in many crops. Therefore, an attempt was made to increase the seed yield in chickpea through the introgression of genes from wild relatives at the International Center for Agricultural Research in the Dry Areas (ICARDA), Syria, from 1987 to 1995. Four crosses, ILC 482 (C. arietinum)×ILWC 179 (C. echinospermum) and ILC 482×ILWC 124 (C. reticulatum) and their reciprocals, were made. Pedigree selection was used to advance the material. Heterosis was recorded visually in F₁s, and single plant measurements for seed yield were recorded in F₂ populations. Promising and uniform progenies were bulked in the F₅ generation. Out of 96 F₆ lines, 22 were selected on the basis of seed yield and other agronomic characters, and evaluated in a replicated trial for seed yield and 14 agronomical, morphological and quality characters. A high level of heterosis was observed in F₁s. Several F₂ plants produced two to three times more seed yield than the best plant from the cultigen. Nine F₇ lines out-yielded the cultigen parent by up to 39%. Over 2 years, 12 lines had a higher yield than the cultigen parent. These lines were not only high yielding but also free of any known undesirable traits from the wild species, such as spreading growth habit, pod dehiscence, and non-uniform maturity. Quality traits, such as seed shape, type, colour, weight, and testa texture, protein content, cooking time and an organoleptic test of a Middle East dish, Homos Bi-Tehineh, were also similar to the cultigen parent. Both C. echinospermum and C. reticulatum contributed towards the increased yield. Received: 11 July 1996 / Accepted: 15 November 1996     

Osmotic adjustment in chickpea (Cicer arietinum L.) results in no yield benefit under terminal drought

Variation in osmotic adjustment (OA) among chickpea (Cicer arietinumL.) cultivars has been observed when exposed to terminal drought,but some studies suggest that this benefits yield while otherssuggest it does not benefit yield in water-limited environments.In the present study, parents differing in OA were crossed anda set of advanced breeding lines (ABLs) developed for yieldtesting. The variation in OA during podding was measured underterminal drought in the F₂, F₃, F₇, and F₈ progeny and in theparents by either rehydrating the leaves before sampling forosmotic potential (OP) or by measuring the relative water content(RWC) and OP on adjacent leaves for the calculation of the OPat full turgor. Yields were measured in the F₈ progeny underterminal drought in Australia and India. While differences inOA were measured in the chickpea lines and parents, OA variedfrom year to year and did not consistently benefit yield whenmeasured in the field under terminal drought. In Australia,differences in OA were not associated with any yield benefitin any year, while in India early flowering resulted in higheryields at three of the four sites, and OA had an inconsistenteffect on seed yields. A comparison of OP at full turgor measuredafter rehydration and from measurements of RWC and OP showedthat the rehydration technique underestimated OA. The lack ofcontribution of OA to yield of chickpea is discussed. Key words: Advanced breeding lines, early flowering, phenology, terminal drought, yield components     

Early generation selection for high yielding cowpea genotypes in additive series intercropping systems with sorghum

Defining appropriate selection strategies for developing cowpea varieties adapted to additive series intercropping systems is an important requirement for cowpea breeders and producers in sub‐Saharan Africa. One hundred and forty‐three F_2:3 cowpea families and their subsequent 99 F_3:4 families derived from a cross between a sole bred cultivar, Apagbaala, and a traditional variety, SARC‐L02, were evaluated under additive series intercropping with sorghum. Intercropping imposed a strong selection pressure for days to flowering such that 31% of F_2:3 families that flowered after 50 days produced too few grains to permit their subsequent evaluation in the F_3:4 generation. Narrow‐sense heritabilities estimated by parent–offspring regression were high for 100 seed weight and days to flowering, moderate for biomass, low for grain yield and insignificant for branches/plant and pods/plant. Retrospective selection at 40% intensity based on F₃ grain yield recovered 5 of the 10 top yielding families in the F₄. No significant difference was observed between mean grain yield of selected and rejected families (at the 40% selection intensity) as estimated by a t‐test. Sole and intercrop yields produced by six advanced breeding lines included as controls showed poor correlation, and suggests selecting cultivars under the target cropping system will produce better selection response.     

Improvement of Rice Biomass Yield through QTL-Based Selection

Biomass yield of rice (Oryza sativa L.) is an important breeding target, yet it is not easy to improve because the trait is complex and phenotyping is laborious. Using progeny derived from a cross between two high-yielding Japanese cultivars, we evaluated whether quantitative trait locus (QTL)-based selection can improve biomass yield. As a measure of biomass yield, we used plant weight (aboveground parts only), which included grain weight and stem and leaf weight. We measured these and related traits in recombinant inbred lines. Phenotypic values for these traits showed a continuous distribution with transgressive segregation, suggesting that selection can affect plant weight in the progeny. Four significant QTLs were mapped for plant weight, three for grain weight, and five for stem and leaf weight (at α = 0.05); some of them overlapped. Multiple regression analysis showed that about 43% of the phenotypic variance of plant weight was significantly explained (P < 0.0001) by six of the QTLs. From F₂ plants derived from the same parental cross as the recombinant inbred lines, we divergently selected lines that carried alleles with positive or negative additive effects at these QTLs, and performed successive selfing. In the resulting F₆ lines and parents, plant weight significantly differed among the genotypes (at α = 0.05). These results demonstrate that QTL-based selection is effective in improving rice biomass yield.     

Introduction of bacterial blight resistance into Triguna,a high yielding,mid-early duration rice variety

Bacterial blight (BB) is a serious disease of rice in India. We have used molecular marker-assisted selection in a backcross breeding program to introgress three genes (Xa21, xa13, and xa5) for BB resistance into Triguna, a mid-early duration, high yielding rice variety that is susceptible to BB. At each generation in the backcross program, molecular markers were used to select plants possessing these resistance genes and to select plants that have maximum contribution from the Triguna genome. A selected BC3F1 plant was selfed to generate homozygous BC₃F₂ plants with different combinations of BB resistance genes. Plants containing the two-gene combination, Xa21 and xa13, were found to exhibit excellent resistance against BB. Single plant selections for superior agronomic characteristics were performed on the progeny of these plants, from BC₃F₃ generation onwards. The selected plants were subjected to yield trials at the BC₃F₈ generation and were found to have a significant yield advantage over Triguna. The newly developed lines are being entered into national multi-location field trials. This work represents a successful example of the application of molecular marker-assisted selection for BB resistance breeding in rice.     

Comparative efficiency of four selection methods for deriving high-yielding lines in mungbean [Vigna radiata (L.) Wilczek]

The comparative efficiency of four selection methods, viz., honeycomb (HC), pedigree selection (PS), single-seed descent (SSD) and the bulk method (BM), was assessed in three crosses of mungbean. The lines derived by each method, along with check varieties, were yield-tested in a compact family block design in F₅ and F₆ generations during summer and kharif of 1990. On the basis of the mean of the lines, the range, the number of superior lines over the best check, and the proportion of the top 10% lines in all the crosses and generations, the honeycomb method exhibited superiority over PS, SSD and BM for yield per plant and its component traits. PS, SSD and BM did not differ from each other. The honeycomb and SSD methods were found suitable for deriving superior lines for seed yield and pods per plant in mungbean.     

Agronomic evaluation of inbred lines derived from tissue cultures of maize

Summary Tissue culture-induced variation has been proposed as a novel source of variation for crop improvement. In maize (Zea mays L.), chromosome aberrations and qualitative genetic variants have been induced during in vitro culture. The proportion of regenerated plants carrying such variants has been shown to increase with culture age. The objective of this research was to evaluate the relationship between culture age and somaclonal variation for several agronomic traits. Six sib-pollinated ears of S₀ (F₂) plants in four OH43 ms/A188 populations each provided control seed and embryos for culture initiation. S₂ lines derived from control seed and from plants regenerated 4 and 8 months after culture initiation were grouped according to their source ear and grown in 6 separate trials. A total of 305 tissue culture-derived and 48 control lines were evaluated as lines per se and in a testcross at each of three locations. Tissue culturederived lines and their testcrosses generally had lower grain yield and moisture. Since grain yield and moisture were not positively correlated in any trial, the highest yielding lines could be selected without increasing grain moisture. Grain yield and plant height tended to decrease with culture age. Although tissue culture-derived lines were, on average, inferior, the highest yielding line per se in three of six trials and the top-ranked line in five of six trials for yield and moisture were derived from tissue culture. The results indicate that tissue culture may generate variation for agronomic traits. Some of the variation, particularly the trend towards earlier maturity, could be useful. However, this method may require screening large populations because of the tendency to generate a large proportion of inferior lines.Contribution from Department of Agronomy and Plant Genetics, University of Minnesota, St. Paul, MN 55108. Minnesota Agric. Exp. Stn. Scientific Journal Series Paper No. 15,172     

Identification and Mapping of Amplified Fragment Length Polymorphism Markers Linked to Shell Color in Bay Scallop, Argopecten irradians irradians (Lamarck, 1819)

Amplified fragment length polymorphisms (AFLP) were used to study the inheritance of shell color in Argopecten irradians. Two scallops, one with orange and the other with white shells, were used as parents to produce four F₁ families by selfing and outcrossing. Eighty-eight progeny, 37 orange and 51 white, were randomly selected from one of the families for segregation and mapping analysis with AFLP and microsatellite markers. Twenty-five AFLP primer pairs were screened, yielding 1138 fragments, among which 148 (13.0%) were polymorphic in two parents and segregated in progeny. Six AFLP markers showed significant (P < 0.05) association with shell color. All six loci were mapped to one linkage group. One of the markers, F1f335, is completely linked to the gene for orange shell, which we designated as Orange1, without any recombination in the progeny we sampled. The marker was amplified in the orange parent and all orange progeny, but absent in the white parent and all the white progeny. The close linkage between F1f335 and Orange1 was validated using bulk segregation analysis in two natural populations, and all our data indicate that F1f335 is specific for the shell color gene, Orange1. The genomic mapping of a shell color gene in bay scallop improves our understanding of shell color inheritance and may contribute to the breeding of molluscs with desired shell colors.     

Improving chickpea yield by incorporating resistance to ascochyta blight

Ascochyta blight [Ascochyta rabiei (Pass.) Lab.] is the most destructive disease of chickpea (Cicer arietinum L.), but it can be managed effectively by the use of resistant cultivars. Therefore, a breeding programme was initiated during 1977–78 at ICARDA, Syria, to breed blight-resistant, high-yielding chickpeas with other desirable agronomic traits. Crosses were made in main season at Tel Hadya, Syria, and the F₁s were grown in the off season at Terbol, Lebanon. The F₂, F₄ and F₅ generations were grown in a blight nursery in the main season where blight epidemic was artificially created. The plants and progenies were scored for blight resistance and other traits. The F₃ and F₆ generations were grown in the off season under normal day length to eliminate late-maturing plants. The pedigree method of breeding was followed initially, but was later replaced by the F₄-derived family method. The yield assessment began with F₇ lines, first at ICARDA sites and later internationally. A total of 1584 ascochyta blight-resistant chickpea lines were developed with a range of maturity, plant height, and seed size not previously available to growers in the blight-endemic areas in the Mediterranean region. These included 92 lines resistant to six races of the ascochyta pathogen, and 15 large-seeded and 28 early maturity lines. New cultivars produced 33% more seed yield than the original resistant sources. The yield of chickpea declined by 340 kg ha^-1, with an increase in blight severity by one class on a 1–9 scale, reaching zero yield with the 8 and 9 classes. Development of blight-resistant lines made the introduction of winter sowing possible in the Mediterranean region with the prospect of doubling chickpea production. Twenty three cultivars have been released so far in 11 countries.Joint contribution from ICARDA and ICRISAT. ICRISAT Journal Article no. JA 1886.     

Comparison of bread wheat lines selected by doubled haploid, single-seed descent and pedigree selection methods

 Yield performance of each group of ten spring bread wheat lines selected by doubled haploid (DH), single-seed descent (SSD) and pedigree selection (PS) methods from three F₁ crosses was compared with the aim of evaluating the DH method in breeding programs. Populations of 65–97 DH lines and 110 SSD lines per cross were used for selection. PS lines were developed by repeated selections from 1500 F₂ plants. Yield evaluation was performed at the F₆ generation of SSD and PS lines along with DH lines in a 2-year field experiment. It took only 2 years from the planting of wheat materials for DH production to the planting of selected DH lines for yield evaluation. There was no significant difference in grain yield between DH lines and PS lines selected from an F₁ cross whose parental varieties were closely related in their pedigrees. In two crosses with low coefficients of parentage and a large variation in their progenies, grain yield of selected DH lines was significantly lower than those of selected SSD and PS lines. These results confirm that the DH method can save time in obtaining recombinant inbred lines ready for yield evaluation. However, a larger DH population is required to achieve the same level of genetic advance with the PS method in crosses containing greater genetic variation. Received: 23 December 1997 / Accepted: 12 March 1998     

Heritability of grain yield,plant height and test weight of a population of winter wheat adapted to Southwestern Ontario

Summary Grain yield, plant height and test weight were studied in a population of winter wheat (Triticum aestivum L.). The population consisted of F₂ bulk populations of 42 crosses among 11 genotypes adapted to S. W. Ontario. Heritabilities were: 0.30±0.32 for yield, 0.77±0.15 for height and 0.98±0.08 for test weight. Predicted genetic gain with 10% selection intensity was 0.15 t/ha for yield, 10.1 cm for height and 3.00 kg/hl for test weight. The low heritability for yield indicates that effective selection would require pedigree information and progeny tests, while the high heritabilities for height and test weight indicate that selection for these traits using single plots would be appropriate.     

Mapping salt-tolerance genes in tomato (Lycopersicon esculentum) using trait-based marker analysis

The germination responsiveness of an F₂ population derived from the cross Lycopersicon esculentum (UCT5) x L. pennellii (LA716) was evaluated for salt tolerance at two stress levels, 150 mM NaCl + 15 mM CaCl₂ and 200 mM NaCl + 20 mM CaCl₂. Individuals were selected at both tails of the response distribution. The salt-tolerant and salt-sensitive individuals were genotyped at 16 isozyme loci located on 9 of the 12 tomato chromosomes. In addition, an unselected (control) F₂ population was genotyped at the same marker loci, and gene frequencies were estimated in both selected and unselected populations. Trait-based marker analysis was effective in identifying genomic locations (quantitative trait loci, QTLs) affecting salt tolerance in the tomato. Three genomic locations marked by Est-3 on chromosome 1, Prx-7 on chromosome 3, and 6Pgdh-2 and Pgi-1 on chromosome 12 showed significant positive effects, while 2 locations associated with Got-2 on chromosome 7 and Aps-2 on chromosome 8 showed significant negative effects. The identification of genomic locations with both positive and negative effects on this trait suggests the likelihood of recovering transgressive segregants in progeny derived from these parental lines. Similar genomic locations were identified when selection was made either for salt tolerance or salt sensitivity and at both salt-stress treatments. Comparable results were obtained in uni- and bidirectional selection experiments. However, when marker allele gene frequencies in a control population are unknown, bidirectional selection may be more efficient than unidirectional selection in identifying marker-QTL associations. Results from this study are discussed in relationship to the use of molecular markers in developing salt-tolerant tomatoes.     

Genetic improvement of egg laying traits in Fayoumi chickens bred under conditions of heat stress through selection and gene expression studies

Thermal stress has been shown to result in decreased egg production, decreased eggshell quality, and ultimately millions of dollars in losses to the industry. Therefore, there are many factors to consider when implementing genetic selection programs aimed at improving egg production under tropical conditions. So, trial is trying to improve the productivity and eggshell quality traits of the Fayoumi chicken under high ambient temperatures via selection programs and gene expression. In the present study, day-old Fayoumi chicks were raised either under normal temperature (control) or conditions of thermal stress (the heated group). At 35 weeks, male and female chickens from the control group were mated randomly and females selected for higher egg production and eggshell strength were mated to male siblings to obtain the progeny of the first generation (F₁). F₁ birds were further selected and mated to obtain the progeny of the second generation. Our results show that egg production and eggshell strength traits improved over successive generations via selection under conditions of heat stress. Furthermore, the reduction in egg production and eggshell strength as a result of heat stress declined from one generation to the next in birds selected for good heat tolerance, and an inverse relationship was observed between the OC-17 and eggshell strength. Additionally, levels of HSP90 and gene expression increased in the two successive generations, indicating that both productivity and heat tolerance were enhanced due to selection in birds raised under conditions of thermal stress. Moreover, generation exerted an important effect on this trait. Thus, desirable traits such as improved heat tolerance in producing lines were observed in Fayoumi chickens exposed to conditions of thermal stress via selection. Therefore, modern advances in studies of poultry breeding and genetics, such as gene expression studies, should be examined.     

Effectiveness of indirect selection for wheat yield in a stress environment

 Effectiveness of indirect selection for grain yield was investigated among eight bread wheat lines, selected in a stress environment in the East African Highlands, where they showed a wide response to yellow rust, the biotic factor causing the stress. The lines were intercrossed to give an 8×8F₁ diallel, which was grown in this same environment for three consecutive growing seasons during 1994 and 1995. Half of the last trial was sprayed with fungicide. From the estimates of narrow-sense heritabilities for yield and yellow rust severity, and the genetic correlation between them, indirect selection for yield in the unsprayed plots, obtained by choosing the most resistant 5% of this material was, on average, 12% higher than selecting for yield itself. In the fungicide-treated plots, indirect selection was only 73% as efficient as direct selection. The implications of these results for selecting for yield in stress environments are discussed. Received: 10 April 1998 / Accepted: 5 August 1998     

The effect of parental divergence on F2 heterosis in winter wheat crosses

Summary In winter wheat (Triticum aestivum L.), the development of a methodology to estimate genetic divergence between parental lines, when combined with knowledge of parental performance, could be beneficial in the prediction of bulk progeny performance. The objective of this study was to relate F₂ heterosis for grain yield and its components in 116 crosses to two independent estimates of genetic divergence among 28 parental genotypes of diverse origins. Genetic divergence between parents was estimated from (a) pedigree relationships (coefficients of kinship) determined without experimentation, and (b) quantitative traits measured in two years of field experimentation in Kansas and North Carolina, USA. These distances, designated (1 -r) and G, respectively, provided ample differentiation among the parents. The 116 F₂ bulks were evaluated at four locations in Kansas and North Carolina in one year. Significant rank correlations of 0.46 (P = 0.01) and 0.44 (P = 0.01) were observed between G and grain yield and kernel number heterosis, respectively. Although (1 -r) was poorly associated with grain yield heterosis, G and midparent performance combined to account for 50% of the variation in F₂ yields among crosses when (1 -r) was above the median value, whereas they accounted for only 9% of the variation among crosses when (1-r) was below the median. Midparent and (1 -r) had equal effects on F₂ grain yield (R ²= 0.40) when G was greater than the median value. A breeding strategy is proposed whereby parents are first selected on the basis of performance per se and, subsequently, crosses are made between genetically divergent parents that have both large quantitative (G) and pedigree divergence (1 -r).Paper No. 12162 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, NC 27695-7643, and Contribution No. 89-396-J of the Kansas Agricultural Experiment Station, Manhattan, KS 66506     

Search for microsatellite markers associated with water-stress tolerance in wheat through bulked segregant analysis

We used bulked segregant analysis (BSA) to identify microsatellite markers associated with water-stress tolerance in wheat. Two DNA pools (tolerant and sensitive) were established from the selected F₂ individuals of crosses between water-stress-tolerant and -sensitive wheat parental genotypes on the basis of the paraquat (PQ) tolerance, leaf size, and relative water content. All three traits were previously shown to be associated with water-stress tolerance on segregating F₂ progeny of the wheat crosses used in this study. Microsatellite analysis was then performed on the established DNA pools, using 35 primer pairs that included all of the chromosome group 5 (5A, 5B, 5D) markers, to detect microsatellite fragments that were present, absent, or both in the DNA pools and their parental lines. We identified one microsatellite fragment that was present in tolerant parent wheat and the tolerant bulk but absent in the sensitive parent wheat and sensitive bulk. We then followed the segregation of this marker in the tolerant F₂ individuals. Use of this marker may significantly enhance the success of selection for PQ- and water-stress-tolerant genotypes in wheat breeding programs.     

Identification and Validation of Quantitative Trait Loci for Agronomic Traits in Advanced Backcross Breeding Lines Derived from Oryza rufipogon × Oryza sativa Cultivar MR219

A backcross breeding strategy was used to identify quantitative trait loci (QTLs) associated with 14 traits in a BC₂F₂ population derived from a cross between MR219, an indica rice cultivar and an accession of Oryza rufipogon (IRGC 105491). A total of 261 lines were genotyped with 96 microsatellite markers and evaluated for plant morphology, yield components and growth period. The genetic linkage map generated for this population with an average interval size of 16.2?cM, spanning 1,553.4?cM (Kosambi) of the rice genome. Thirty-eight QTLs were identified with composite interval mapping (CIM), whereas simple interval mapping (SIM) resulted in 47 QTLs (LOD >3.0). The O. rufipogon allele was favourable for 59% of QTLs detected through CIM. Of 261 BC₂F₂ families, 26 advanced backcross breeding lines (BC₂F₅) were used for QTL validation. These lines were selected on the basis of the yield traits potentiality in BC₂F₃ and BC₂F₄ generations. The field trial was conducted at three different locations in Malaysia using randomized complete block design with three replications. Trait based marker analysis was done for QTL determination. Twenty-five QTLs were detected in BC₂F₅ generation whereas 29 QTLs were detected in BC₂F₂ generation of the same population. Two QTLs (qPL-1 and qSPL-7) were not considered for validation due to their low R ² values and two QTLs (qPSS-3-2 and qGW-3-2) were not detected in the BC₂F₅ population. Fifteen QTLs showed the beneficial effect to enhance the trait value of the breeding lines. QTL validation aided to select the promising lines for further utilization.     

Intersubgenomic heterosis in seed yield potential observed in a new type of Brassica napus introgressed with partial Brassica rapa genome

This paper reports the observation on the intersubgenomic heterosis for seed yield among hybrids between natural Brassica napus (AⁿAⁿCⁿCⁿ) and a new type of B. napus with introgressions of genomic components of Brassica rapa (A^rA^r). This B. napus was selected from the progeny of B. napus × B. rapa and (B. napus × B. rapa) × B. rapa based on extensive phenotypic and cytological observation. Among the 129 studied partial intersubgenomic hybrids, which were obtained by randomly crossing 13 lines of the new type of B. napus in F₃ or BC₁F₃ to 27 cultivars of B. napus from different regions as tester lines, about 90% of combinations exceeded the yield of their respective tester lines, whereas about 75% and 25% of combinations surpassed two elite Chinese cultivars, respectively. This strong heterosis was further confirmed by reevaluating 2 out of the 129 combinations in a successive year and by surveying hybrids between 20 lines of the new type of B. napus in BC₁F₅ and its parental B. napus in two locations. Some DNA segments from B. rapa were identified with significant effects on seed yield and yield components of the new type of B. napus in BC₁F₅ and intersubgenomic hybrids in positive or negative direction. It seems that the genomic components introgressed from B. rapa contributed to improvement of seed yield of rapeseed.     

Anther and tissue culture-induced grain chalkiness and associated variants in rice

Rice, Oryza sativa, plants regenerated from anther culture with and without in vitro selection pressure were evaluated for chalky seed. Progeny evaluated included 21 spontaneously doubled haploids selfed 4 times, progeny from plants regenerated from S-aminoethylcysteine resistant callus selfed 4 times and backcrosses of both types to the parental type. All lines with in vitro histories had higher seed chalkiness than the controls both in the intensity of chalkiness and in the number of seeds expressing the character. The full range of intensity and amount of chalkiness was expressed in the progeny. The average intensity of anther/tissue culture-derived progeny was 4–5, based on a scale of 1 (translucent) to 10 (fully opaque), and the average amount of chalkiness within plants sampled was 50–75 percent. The chalky characteristic is transmitted from parent to offspring into a range of identifiable F₂ segregants. Disclaimer statement Mention of a trademark or proprietary product does not constitute a guarantee or warranty of the product by the USDA, and does not imply its approval to the exclusion of other products that may also be suitable.