major genetic factors and to be highly heritable ( Svejda, 1979 ). As a result, large gains from selection can be made when hybridizing hardy parental genotypes ( Zlesak, 2007 ). A recent QTL mapping study suggested the potential existence of a major QTL
Cindy Rouet, Joseph O’Neill, Travis Banks, Karen Tanino, Elodie Derivry, Daryl Somers, and Elizabeth A. Lee
Peter M. Hanson, Jen-tzu Chen, and George Kuo
High-temperature fruit set (heat tolerance) is a critical trait of tomato (Lycopersicon esculentum Mill.) cultivars targeted for lowland wet season production in the tropics and subtropics. Heat-tolerant Asian Vegetable Research and Development Center (AVRDC) tomato line CL5915-93D4-1-0-3 (CL5915) is a valuable source of heat-tolerance genes for tomato genetic improvement. The gene action of heat tolerance in CL5915 was determined by evaluating the F1, F2, BCP1, and BCP2 of a cross between CL5915 and heat-sensitive line UC204A for fruit set traits in two wet-season trials at AVRDC. Parent-offspring regression of F2-derived F3 (F2:3) family means on the F2 plants from CL5915 × UC204A was used to estimate the heritability of F2 single plant selection for heat tolerance. Mean percentage of fruit set and fruit number per cluster of the F1 and BCP1 exceeded midparent values and were not significantly different from those of CL5915, indicating complete dominance for heat tolerance. Generation means analyses indicated that a model including simple additive and dominance effects adequately explained the inheritance of mean fruit number per cluster both years. For mean percentage of fruit set, a model including simple additive-dominance effects produced an adequately fitting model in the 1996 season but the best-fitting model included an epistatic component in the 1997 season. Heritabilities estimated for fruit set traits in 1996 and 1997, respectively, were: 0.31 and 0.21 for percentage of fruit set; 0.28 and 0.14 for mean fruit number per cluster; and 0.53 and 0.15 for flower number per cluster. The low heritabilities for percentage of fruit set and mean fruit number per cluster under high temperatures imply that single plant selection in the F2 for heat tolerance from crosses involving CL5915 is not effective and that selection should be based on replicated family testing in the F3 and later generations.
R. Bruce Carle and J. Brent Loy
Genetic experiments were initiated to assess the potential for combining large seed size from PI 285611, a large-fruited, hullless seeded accession, with small fruit size from a hullless seeded breeding line (NH29-13-5-4). An F2 population and parental line were field-grown during Summer 1993 to determine inheritance and heritability of large seed size and the relation between fruit and seed size. Seed size variables of weight, width, length, and thickness were regressed against fruit weight. There was a moderate, positive correlation between large fruit and seed length (R2 = 0.46). However, seed thickness, a major determinant of seed weight, was not correlated with fruit size. In an F2 population of ≈450 plants, there was a small number of plant selections with fruit under 1.5 kg and seed size approaching that of PI 285611.
Alfred Jones and P. D. Dukes
Three greenhouse tests to determine the reactions of sweet potato (Ipomoea batatas (L.) Lam.) breeding lines and their respective open-pollinated offspring to 2 species of root-knot nematodes were conducted. Resistances occurred in high frequency to both the southern root knot nematode (Meloidogyne incognita (Kofoid & White) Chitwood) and the Javanese (tropical) root knot nematode (M. javanica (Treub) Chitwood). Reaction to M. incognita was studied in 2 consecutive years with different sets of parental lines using an egg mass index. Estimated heritability (h2) in 1976 was 0.75 ± 0.23 and in 1977 was 0.57 ± 0.37. Three indices of reaction to M. javanica and respective h2 estimates were: Egg mass index, 0.69 ± 0.18; galling index, 0.78 ± 0.19; and necrosis index, 0.72 ± 0.20. Resistances to the 2 species were not correlated, indicating independent inheritance. Development of cultivars with high levels of resistance to each or to both of the above diseases is possible.
Ahmed A. Hassane, Donald H. Wallace, and Robert E. Wilkinson
The inheritance of resistance to Fusarium solani f. phaseoli Kend. & Sny.) in Phaseolus vulgaris lines P. I. 203958 (N203), and 2114-12 which derives its resistance from P. coccineus, was studied under greenhouse and field conditions. It was concluded that: N203 and 2114-12 respectively possess 4 and 5-6 genes for resistance under the greenhouse-test conditions used; 4 of the 2114-12 genes for resistance are the same as the N203 genes; gene action is mostly additive but partial dominance of resistance appears in 9-13-week-old field-tested plants. Broad sense heritability was estimated as 62-64% under greenhouse conditions and as 22% and 79%, respectively, in 5 and 9-13-week-old field tested plants. The additive variance under greenhouse conditions was estimated as 72% and 40% respectively for resistance from 2114-12 and N203.
Bruce H. Barritt
Red raspberry (Rubus idaeus L.) fruit firmness, measured as compression force with a Hunter Series L portable pressure gauge, was determined from 15 parent clones and for 813 seedlings derived from 44 crosses. Heritability estimate for fruit firmness, based on parent/offspring regression, was .90 ± .13. Analysis of variance of progeny data showed that general combining ability variance (additive) was significant and much larger than specific combining ability variance. Of the parent clones, ‘Glen Isla’, ‘Glen Prosen’, SHRI6820/41, and SHRI6820/64 had the firmest fruit and, on the basis of progeny analysis, had the highest general combining ability parent values. Low parental values were obtained for ‘Sumner’, ‘Mailing Leo’, ‘Mailing Admiral’, ‘Taylor’, ‘Haida’, and ‘Meeker’.
Ann Marie Connor, James J. Luby, and Cindy B.S. Tong
Narrow-sense heritability and among-family and within-family variance components were estimated for antioxidant activity (AA), total phenolic content (TPH), and anthocyanin content (ACY) in blueberry (Vaccinium L. sp.) fruit. AA, TPH, and ACY were determined in the parents and in 10 offspring from each of 20 random crosses for each of 2 years at Becker, Minn. Offspring-midparent regression analysis provided combined-year heritability estimates of 0.43 ± 0.09 (P ≤ 0.0001) for AA, 0.46 ± 0.11 (P ≤ 0.0001) for TPH, and 0.56 ± 0.10 (P ≤ 0.0001) for ACY. Analyses of variance delineated variation among and within families for AA, TPH, and ACY (P ≤ 0.001). Year-to-year variation in the means for all offspring genotypes was not significant for AA or TPH, but there were changes in rank between years for families and for offspring within families for these traits. Year-to-year variation in the mean for all offspring genotypes was significant for ACY, but rank changes were observed only among offspring within families, not among families. In total, 18 of 200 offspring from 7 of the 20 crosses were transgressive segregants for AA, exceeding the higher parent of the cross by at least two sds. Estimates of variance components showed that variation among families accounted for 24% to 27% of total variance for the three traits. However, variation within families was greater than that among families, accounting for 38% to 56% of total variance for the three traits. These results suggest that increasing antioxidant activity in blueberry through breeding is feasible, and that the breeding strategies utilized should exploit the large within-family variation that exists.
Ahmed R. Aggour and Dermot P. Coyne
Common blight in beans (Phaseolus vulgaris L.) incited by Xanthomonas campestris pv. phaseoli (Smith) Dye (X c p) reduces crop yield and seed quality. The objective of this experiment was to study heritability and phenotypic correlations of the disease reaction to various strains of X c p at several plant developmental stages in specific bean crosses using diverse methods of inoculation. Leaf and pod disease reactions to strains of X c p were inherited quantitatively and narrow-sense heritability estimates were low in the following crosses between Phaseolus vulgaris cultivars/lines: Bac-6 (moderately resistant = MR) × NE-EP1 (MR); Bat-862 (MR) × ‘Pompadour Checa’ (susceptible = S); ‘Pompadour Checa’ (S) × Bac-6 (MR); ‘Venezuela 44’ (S) × Bat-862 (MR). Pod disease reaction was not correlated with leaf disease reaction at any growth stage. Low or nonsignificant phenotypic correlations were detected between disease reactions of leaves at the seedling and flowering stages with the several methods of inoculation. Intermediate phenotypic correlations were found for disease reactions with three methods of inoculation at the seedling stage, but only with two methods in the flowering stage. Negative or nonsignificant phenotypic correlations were observed between leaf disease reaction and number of days to first flower. Different duplicate recessive genes were found to control two foliar abnormality traits: crippled growth and variegated leaves. No plants with a combination of both traits were observed. An association was found between crippled growth and a high level of resistance to strain V3S8 of X c p in the cross Bat-862 × ‘Pompadour Checa’.
Thomas A. Greene
Height and caliper (age 3 years), and flower count (age 3.5 years) were evaluated for 36 open-pollinated families of Magnolia grandiflora L. outplanted in two genetic tests in Bexar County, Texas. Significant family differences existed for height, caliper, number of flowers per tree, and percent of trees flowering in both tests. Family heritability estimates for all traits ranged from 0.72 to 0.92. Coefficients of genetic prediction (CGP) between growth and flowering characteristics were small but positive; CGP between height and percent of trees flowering was 0.28 and 0.24 in the two tests. Early growth rate and flowering appeared to be under strong genetic control; thus, improvement through selection would be efficient. However, both traits should be evaluated since the genetic relationship between them was weak.
B. H. Barritt, P. C. Crandall, and P. R. Bristow
Red raspberry (Rubus idaeus L.) clones and seedlings were evaluated in infested field soils for resistance to a root rot. Disease symptoms were root necrosis and wilting of first and second year canes. Of 41 clones examined ‘Latham’, ‘Newburgh’, ‘Durham’, ‘Chief’ and ‘WSU 458’ were the most resistant. ‘Lloyd George’ and its derivatives were generally the most susceptible. Evaluation of seedlings from 25 crosses showed that ‘Latham’ and ‘Newburgh’ produced the highest percentage of resistant seedlings and the seedlings with the highest level of resistance; ‘Glen Clova’ and ‘Meeker’ produced the fewest seedlings with resistance. Heritability estimates based on parent/offspring regression were 0.85 for the percentage of seedlings infected and 0.92 for the mean seedling injury rating.