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Abstract

The inheritance of tolerance to rhizoctonia fruit rot incited by Rhizoctonia solani Kuhn differed depending upon the source of the plant material of tomato (Lycopersicon esculentum Mill.). The tolerance in USDA 75B 846-1-1 was controlled by 1 major gene without dominance. The tolerance in USDA 75B 610-3 was polygenic with 4 major genes. Tolerance in USDA 75B 846-1-1 had a narrow-sense heritability of 71% while in USDA 75B 610-3 heritability was 30%. Fruit rot tolerance and resistance to puncture pressure were highly correlated in both families. Fruit shape and fruit rot tolerance were also highly correlated in the family with USDA75B 846-1-1.

The root-knot nematode (M. hapla Chitwood) poses a threat to carrot (Daucus carota L.) production in the United States. Little information is available concerning the genetic control of nematode resistance in carrot. Crosses between two inbreds, a resistant genotype (R₁) and susceptible genotype (S₁) identified in previous screening tests of carrot were studied in the F₂ and BC₁ generations to determine the heritability of resistance to the root-knot nematode. Seedlings of F₂ (R₁/S₁), BC₁S₁, and BC₁R₁ generations were evaluated for their responses to infestation of M. hapla Chitwood based on gall number per root, gall rating per root, and root rating per root in a greenhouse experiment conducted during 1994. Narrow-sense heritabilities were calculated according to the method of Warner (1952). Narrow-sense heritability was 0.16 for resistance based on gall number, 0.88 for resistance based on gall rating, and 0.78 for resistance based on root rating. This information may be of importance to geneticists and carrot breeders for the development of nematode-resistant carrot cultivars.

Narrow-sense heritabilities for reaction to chlorotic leaf distortion (CLD), incited by Fusarium lateritium Nees: Fr., were estimated in sweetpotato [Ipomoea batatas (L.) Lam] by variance component analysis and parent–offspring regression. Visually rated severity reactions to CLD varied greatly among the 20 parents used to generate half-sib progeny from open-pollinated nurseries in 1990 and 1991. Progeny from each nursery were evaluated along with parents in a completely randomized design in two consecutive years. Narrow-sense heritability (h ²) estimates based on variance components were moderate on an entry mean basis at 0.61 in 1990, 0.38 in 1991, and 0.33 for the two years combined. Slightly higher, but still moderate, estimates were obtained on an individual plant basis. Narrow-sense heritability estimates using parent–offspring regression were 0.35 in 1990, 0.33 in 1991, and 0.33 for the two years combined. Predicted next-generation response was highest using a half-sib family recurrent selection among three schemes compared at a 10% selection intensity. Our data indicate –0.63 improvement in the half-sib family CLD severity rating in one breeding cycle.

Abstract

Data from 14 traits in muskmelon (Cucumis melo L.) were analysed by parent-offspring regression to produce estimates of heritability and phenotypic, genotypic, and environmental correlations. Heritability estimates determined from correlation coefficients (h² = r), equivalent to regression analysis on data coded in standard deviation units (h² = b¹), were low (5–13%) for maturity and yield traits, and moderate (53–71%) for fruit appearance and quality traits. Soluble solids content at h² = 16% was the exception. Heritabilities calculated by intraclass correlations of half-sib progenies (h² = 4t_hs) provided many values which exceeded 100%. Phenotypic, genotypic and environmental correlations among paired traits indicated many significant and desirable relationships which could be used to reduce numbers of observations on breeding materials as well as provide guidance for selection within future muskmelon populations. Correlated responses were predicted for all traits from single-trait selection of several fruit quality characters. Predicted and realized responses in the offspring generation by simulated direct selection (10%) for each character within the parent population are presented. Priorities for trait selection and choice of breeding procedures for improvement in muskmelon are discussed. External fruit characters such as net appearance and nonindented vein tracts, or intermediate fruit size, each of which can be scored visually and rapidly, appear most suited for selection within these populations.

Abstract

Strawberry (Fragaria × ananassa) seedlings were evaluated for yield, fruit weight, and commercial appearance in two field trials established in 1985 and 1986. Genetic analyses for unbalanced diallels were performed to quantify genetic, environmental, and interaction variance for each trial separately, and for crosses common to two locations in a single year. When data from crosses common to two test locations were analyzed simultaneously, narrow-sense heritabilities (h²) averaged 0.35 (±0.11), 0.21 (±0.07), and 0.08 (±0.06) for yield, fruit weight, and appearance score. Broad-sense heritabilities (H²) were 0.35 (±0.11), 0.27 (±0.12), and 0.21 (±0.11) for the same traits, respectively. These estimates do not differ significantly from heritabilities estimated from the ancestral breeding population 20 years ago. Estimates of H² for single-location analyses were biased upwards by dominance × location interactions for all traits. Additive × location interactions were detected for appearance score and contributed a small bias to single-location estimates of h². Use of biased estimates in predicting genetic gain could lead to errors in choice of appropriate selection strategy.

The genetic opportunity for selection of early fruiting strawberry cultivars was evaluated using seedling populations from the Univ. of California (UC) breeding program in three years. Narrow-sense heritabilities for early season yield and for the proportion of an individual's total yield expressed early were moderate (h² = 0.24-0.53) and broad-sense heritabilities were slightly larger (H² = 0.31-0.70), suggesting the presence of some nonadditive genetic variance for these traits. These two traits were genetically correlated with each other (r_g = 0.78-0.98), but only early yield was consistently genetically correlated with seasonal yield (r_g = 0.52-0.82). Selection was performed for each trait using an index on full-sib family means and individual phenotypic values in two of the three years, and predicted response was compared with that obtained using vegetatively propagated runner plants from selected genotypes in the subsequent fruiting season. Statistically significant (P < 0.05) selection response was obtained in one of two years for each trait, and combined analysis demonstrated highly significant (P < 0.01) response for both traits. However, realized response over all traits and years was just 27.3% of that predicted based on the estimated heritabilities and applied selection intensities. These results suggest that selection for early yield should be based at least in part on runner plant evaluations rather than exclusively on seedling performance.

Abstract

Resistance to T. basicola was found in Phaseolus vulgaris lines P.I.203958 (N203) and 2114-12. To determine the inheritance of resistance, these 2 lines were crossed with each other and with the susceptible cv. Redkote. Greenhouse tests were conducted on parental, F₁, F₂, and backcross progenies of each of the 3 crosses, and on F₃ progenies of crosses ‘Redkote’ × 2114-12 and ‘Redkote’ × N203. The data indicate that N203 and 2114-12 possess the same genes for resistance, that resistance is partially recessive, and that resistance is controlled by approximately 3 genes. Broad sense heritability was estimated as 59% and the additive variance as 39%.

Abstract

Resistance to Trichoplusia ni (Hubner), Pieris rapae (L.), and Plutella xylostella (L.) in cabbage [Brassica oleracea L. (Capitata group)] and cauliflower (B. oleracea, Botrytis group) was studied using a 5-parent diallel. Resistance was quantitatively inherited without undesirable linkages. When Plant Introduction (PI) 234599 (a glossy-leaved cauliflower) was used as a parent, narrow sense heritabilities of 22-47% were obtained for resistance. This resistance was maintained irrespective of plant age or presence or absence of alternate oviposition hosts. Plants with moderate tolerance only express it at maturity. The highest levels of resistance were transferred with difficulty into desirable type cauliflower and cabbage with slight bloom.

Abstract

Early blight resistance was estimated in field plots for parents and F₁, F₂, and backcross progenies of crosses with NC EBR-1, a line derived from Lycopersicon hirsutum P.I. 126445. Areas under the disease progress curve (AUDPC) showed that resistance from NC EBR-1 was heritable and quantitative in nature. generation means in two families were intermediate to those of NC EBR-1 and susceptible parents. The distribution of AUDPC means for the different generations in both families indicated the presence of epistasis or gene linkage. Lack of fitness tests for curve-linearity confirmed this in one family. A, B, and C scaling tests showed similar results. A joint three-factor model and subsequently a six-factor model displayed the presence of epistasis in both families. Ignoring epistatic effects, narrow-sense heritability (h²) was 0.49 in one family and 0.40 in the other. By regressing F₃ progeny AUDPC means on selected F₂ plant values, h² was 0.25 and 0.17, respectively.

Pericarp thickness in maize (Zea mays L.) was analyzed by generation mean analysis for backcross and F₂ populations from eight hybrids, derived from two thin-pericarped sweet corn inbreds—AA8 and 677a (55 and 51 μm)—crossed with four field corn inbreds—B37, B68, H55, and Hi26 (range 82-132 μm). Average heterosis was −12.5% and segregating progeny distributions were skewed toward those of thin-pericarped parents. Narrow-sense heritability was high, averaging 55.2%, and the number of effective factors was low, ranging from 1.4 to 5.9 and averaging 3.3. Epistatic effects were as large as additive or dominance effects in many crosses, urging caution in applying models that exclude gene interactions to determine variance components and heritabilities. The mode of action in reducing pericarp thickness appeared to differ among the two thin parents, with AA8 affecting the differential thickening of germinal vs. abgerminal walls, and 677a reducing the number of pericarp cell layers. All genetic parameters suggested that genetic progress in backcross conversions to thin pericarp in sweet corn breeding would be rapid irrespective of the pericarp thickness of exotic parents.