Tomato mottle virus (ToMoV) is a silverleaf whitefly (Bemisia argentifolii Bellows and Perring n. sp.) transmitted, bipartite geminivirus that infects tomatoes (Lycopersicon esculentum Mill.). Inbred lines resistant to ToMoV were derived from Lycopersicon chilense Dunal accession LA 1932. Inheritance was studied using a family developed from the crossing of a resistant inbred with a susceptible tomato inbred over two seasons. The F1 had resistance intermediate to the parents and generation means analysis of F1 and F2, backcross and parental populations suggested that the action of at least two additive genes with high heritability (h2 n.s. = 0.87) controlled ToMoV resistance. When data from the two seasons were combined, an acceptable fit to an additive-dominance genetic model was obtained. Single plant comparisons, bulk comparisons, and tailends of F2 populations segregating for ToMoV resistance derived from LA 1932 identified randomly amplified polymorphic DNA (RAPD) markers using eight hundred 10-mer oligonucleotide primers. The F2 populations used for inheritance studies were screened for polymorphic markers, and 12 RAPD markers associated with the ToMoV resistant line were linked to the morphological markers self-pruning (sp) and potato leaf (c) on chromosome 6. RAPD markers that were associated with ToMoV resistance segregated into two linked regions flanking either side of the sp and c loci. The molecular studies suggested that the action of at least two additive regions controlled ToMoV resistance which supported the inheritance analysis.
P.D. Griffiths and J.W. Scott
A. Rodríguez-Burruezo, J. Prohens, and F. Nuez
Twenty-six clones of pepino (Solanum muricatum Aiton) were evaluated for yield, fruit weight, fruit shape (length to width ratio), soluble solids concentration (SSC), titratable acidity (TA), and ascorbic acid concentration (AAC) over two growing seasons: autumn-winter (AW) and spring-summer (SS). Significant differences were found for the effects of clone, season, and clon× season interaction for all traits, except in the case of season for fruit shape. Mean values for yield, SSC, and AAC were higher in the AW than in the SS season, while mean fruit weight and TA were lower. Many clones (13 in AW and six in SS) had a yield higher than 30 t·ha-1. Substantial genotypic variation was found for all traits studied except for SSC. Clones stable for all traits were detected over both seasons, except for SSC, where the differences between seasons were very high. The significant clone × season interaction for all traits indicates that selection of genotypes adapted specifically to either AW or SS seasons would maximize the response to selection. Broad sense heritabilities were highest for fruit shape and yield (>0.70), while SSC had the lowest values (0.39 in AW, 0.17 in SS, and almost 0 when considering both seasons combined). For the AW season, significant fruit weight-SSC and fruit weight-AAC genotypic correlations were detected; for the SS season the significant genotypic correlations were yield-SSC, fruit weight-TA, fruit shape-TA, and SSC-TA. Results suggest there are ample opportunities for improving several traits in this crop using intraspecific variation for adaptation to specific environments.
Craig Hardner, João Costa e Silva, Emlyn Williams, Noel Meyers, and Cameron McConchie
between seedling and grafted plants, after removal of a general average propagation effect. Narrow-sense heritability and individual broad-sense heritability were estimated for each trait at the t th trial by p th density as: h t p 2 = v A s p v A s p
Creighton L. Gupton and James M. Spiers
A study of leaf chlorosis in rabbiteye blueberries (Vaccinium ashei Reade) grown in soil containing 300 to 400 ppm diethylenetriaminepentaacetic acid (DTPA)-extracted Mn revealed no relationship between leaf Mn content and chlorosis. A second study was conducted to estimate heritability of the content of Mn, Fe, and certain other mineral elements that have been associated with leaf chlorosis and to determine the genetic relationships among shoot dry weight, visual rating, and the mineral elements in rabbiteye blueberry. Heritability estimates were high for all variables except Fe, suggesting that changes in Mn, Zn, Ca, Mg, or K contents could be expected from phenotypic recurrent selection. However, manipulation of mineral content probably would not ameliorate the Fe chlorosis. The high heritability of shoot dry weight and visual rating and the high genetic correlation between these variables suggest that plants resistant to mineral effects on Fe metabolism can be selected on the basis of visual rating.
Creighton L. Gupton and Barbara J. Smith
Experiments were conducted to estimate the relative importance of additive and dominance genetic variances and non-allelic interactions in the inheritance of resistance to Colletotrichum spp. in strawberry (Fragaria × ananassa Duch.). Progeny of 40 parents crossed in a Comstock and Robinson Design II Mating scheme were inoculated with three isolates of C. fragariae and one isolate of C. acutatum. Disease development on each plant was rated visually. Variance components were estimated and converted to genetic variances. Estimates of were six to 10 times higher than those for Within-family variance not accounted for by equaled 35% and 38% of the total genetic variance in females and males, respectively, indicating probable epistatic effects. The frequency distribution of disease severity ratings was bimodal in both experiments, suggesting major gene action. Narrow-sense heritability estimates were 0.37 and 0.26, and broad-sense heritability estimates were 0.87 and 0.85 for females and males, respectively. Narrow-sense heritability estimates are probably sufficient to produce gains from recurrent selection. Gains from selection of clonal value should be possible because of the high broad sense heritability estimates. It appears feasible to establish a broad genetic-based population resistant to Colletotrichum spp. from which selections could be evaluated per se and/or recombined to produce improved populations.
Steven M. Todd, Van-Den Truong, Kenneth V. Pecota, and G. Craig Yencho
heritability estimates. Family diversity. Cultivated sweetpotato (2n = 6x = 90) is widely recognized as a diverse species and the 25 full-sib families, of 20–25 progeny each, generated in this experiment demonstrated extensive diversity for storage root shape
A.B. Herriott, F.L. Haynes Jr., and P.B. Shoemaker
Heritability of resistance to early blight disease in potatoes (Solarium tuberosum L.) incited by Alternaria solani (En. & Martin) Ser. was estimated in tetraploid × diploid crosses. Susceptible tetraploid cultivars and breeding lines were the female parents. Diploids that produced a high proportion of first-division restitution (FDR) gametes and possessed different levels of early blight resistance were the male parents. Tubers from seedlings that resulted from the tetraploid × diploid crosses were planted in a field and artificially inoculated with spores of Alternaria solani. Resistance was measured as the slope (r) of the regression of the logit of the percent defoliation of each plant vs. time. Higher r values indicated lower resistance. Mean r values ranged from 0.123 to 0.157 for the tetraploid parents, and from 0.054 to 0.116 for the diploid parents. Mean r values for the tetraploid × diploid crosses were intermediate, ranging from 0.077 to 0.143. Narrow-sense heritability (h2) was 0.815. The partial correlation coefficient between r and mean maturity values was – 0.2086.
Valdomiro A.B. de Souza, David H. Byrne, and Jeremy F. Taylor
Thirteen peach [Prunus persica (L.) Batsch] fruit characteristics were investigated for 3 years, 1993, 1994, and 1995, in College Station, Texas, to determine heritability, genetic and phenotypic correlations, and predicted response to selection. Seedlings of 108 families resulting from crosses among 42 peach cultivars and selections were used in the evaluations. A mixed linear model, with years treated as fixed and additive genotypes as random factors, was employed to analyze the data. Best linear unbiased prediction (BLUP) was used to estimate fixed effects. Restricted maximum likelihood (REML) was used to estimate variance components, and a multiple trait model was used to estimate genetic and phenotypic covariances between traits. Genetic and phenotypic correlations ≥0.65 and <0.30 were considered strong or very strong and weak, respectively. Date of ripening, fruit development period (FDP) and date of full bloom had the highest heritability (h2) estimates, 0.94, 0.91, and 0.78, respectively. Fruit cheek diameter and titratable acidity (h2 = 0.31) were the traits with the lowest estimates. Fruit development period, fruit blush, and date of ripening had the highest predicted selection responses, whereas fruit suture, fruit cheek, L/W12 (ratio fruit length to average fruit diameters), and fruit tip had the lowest values. Most genetic correlations were ≥0.30 and were, in general, much higher than the corresponding phenotypic correlations. All four measures of fruit size were genetically and phenotypically very strongly correlated. Important genetic correlation estimates were also observed for date of ripening with FDP (ra = 0.93), date of ripening and FDP with fruit blush (ra = -0.77, ra = -0.72), SS (percent soluble solids) (ra = 0.63, ra = 0.62) and TA (ra = 0.55, ra = 0.64), and SS with TA (ra = -0.56). Direct selection practiced solely for early ripening and short FDP is expected to have a greater effect on correlated traits than direct selection for early bloom and large fruit mass.
Chih-Cheng T. Chao, Dan E. Parfitt, and Themis J. Michailides
Pistachio (Pistacia vera L.) progeny were evaluated at two locations in California for resistance to alternaria late blight caused by Alternaria alternata (Fries) Keissler in 1995 and 1997. Large differences in alternaria late blight infection among seedlings were observed. Narrow sense heritabilities based on half-sib analysis of 20 open pollinated families were 0.48 and 0.11 at Kearney Agricultural Center in 1995 and 1997, respectively, and 0.56 and 0.54 at the Wolfskill Experimental Orchard near Davis in 1995 and 1997, respectively. Differences among families to alternaria late blight infection were highly significant and associated with the female parents. Fifty-eight highly resistant seedlings were identified for future cultivar selection efforts.
Frank M. Elia, George L. Hosfield, James D. Kelly, and Mark A. Uebersax
A knowledge of the relative proportion of additive and nonadditive genetic variances for complex traits in a population forms a basis for studying trait inheritance and can be used as a tool in plant breeding. A North Carolina Design II mating scheme was used to determine the inheritance of cooking time, protein and tannin content, and water absorption among 16 genotypes of dry bean (Phaseolus vulgaris L.) representative of the Andean Center of Domestication. Heritability and the degree of dominance for the traits were also calculated to provide guidelines for adopting breeding strategies for cultivar development. Thirty-two progeny resulted from the matings and these were assigned to two sets of 16 progeny each. Variances due to general combining ability (GCA) and specific combining ability (SCA) were significant for the traits. The GCA was larger in all cases. Narrow-sense heritability for protein, tannin, water absorption, and cooking time averaged 0.88, 0.91, 0.77, and 0.90, respectively. Degree of dominance estimates indicted that the traits were governed by genes with partial dominance except, in one case, tannin had a degree of dominance value of zero, indicating no dominance. The phenotypic correlation (-0.82) between water absorption and cooking time justifies using the water absorption trait as an indirect selection method for cooking time. With regard to parent selection in crosses, significant differences between GCA females and GCA males suggested cytoplasmic influences on trait expression. Hence, the way a parent is used in a cross (i.e., as female or male) will offset trait segregation. Using fast-cooking bean cultivars in conjunction with fuel-efficient cooking methods may be the best strategy to conserve fuelwood and help reduce the rate of deforestation in East and Central Africa.