The genetic basis for heat tolerance during reproductive development in snap bean was investigated in a heat-tolerant × heat-sensitive common bean cross. Parental, F1, F2, and backcross generations of a cross between the heat-tolerant snap bean breeding line `Cornell 503' and the heat-sensitive wax bean cultivar Majestic were grown in a high-temperature controlled environment (32 °C day/28 °C night), initiated prior to anthesis and continued through plant senescence. During flowering, individual plants of all generations were visually rated and scored for extent of abscission of reproductive organs. The distribution of abscission scores in segregating generations (F2 and backcrosses) indicated that a high rate of abscission in response to heat stress was controlled by a single recessive gene from `Majestic'. Abscission of reproductive organs is the primary determinant of yield under heat stress in many annual grain legumes; this is the first known report of single gene control of this reaction in common bean or similar legumes. Generation means analysis indicated that genetic variation among generations for pod number under heat stress was best explained by a six-parameter model that includes nonallelic interaction terms, perhaps the result of the hypothetical abscission gene interacting with other genes for pod number in the populations. A simple additive/dominance model accounted for genetic variance for seeds per pod. Dominance [h] and epistatic dominance × dominance [l] genetic parameters for yield components under high temperatures were the largest in magnitude. Results suggest `Cornell 503' can improve heat tolerance in sensitive cultivars, and heat tolerance in common bean may be influenced by major genes.
Katy M. Rainey and Phillip D. Griffiths
Kevin M. Crosby
Improving melon root systems by traditional breeding is one component of the program to develop multiple-stress-resistant melons at the Texas Agricultural Experiment Station, Weslaco. Ten diverse melon lines representing four horticultural groups were intercrossed utilizing a Design II mating scheme. The male parents were: `PI 403994,' `Perlita,' `Doublon,' `Caravelle', and `PI 525106.' The female parents were: `Créme de Menthe,' `Magnum 45,' `BSK,' `PI 124111 × TDI', and `Deltex.' F1 progeny were grown in pasteurized sand in the greenhouse using a randomized complete-block design with four reps. After 4 weeks, root systems from all plants were carefully washed to remove the sand. Each root system was then placed onto a glass, plated, and scanned into the computer software Rhizo Pro 3.8 (Regent Instruments, Quebec). This software calculated root lengths of various diameter classes, root area, and root tip number. All data was input into Agrobase software for calculation of genetic variances based on Design II analysis. Significant differences of contributions by male parents to progeny variation were few. Only length of roots with 1.0- to 1.5-mm-diameter and vine length were significantly different. Differences in contributions by female parents to all traits except root tip number were highly significant. No significant interaction effects were observed for any trait. Narrow-sense heritability estimates were moderate to high for all traits. The range was from 0.56 for root tip number by males to 0.81 for both length of 0.5- to 1.0-mm-diameter roots and vine length for females. Estimates for total root length (0.76) and root surface area (0.77) were high. The lack of male by female interaction suggests very low dominance genetic variation and contributed to high heritability estimates, which represent predominantly additive gene action. Additive genetic variation allows more-efficient progress by selection, making the potential for root system improvement favorable.
Bridget K. Behe, Rachel M. Walden, Marcus W. Duck, Bert M. Cregg, Kathleen M. Kelley, and R.D. Lineberger
An aging American population may be less willing than a younger population to install and remove a live, fresh-cut evergreen tree in their home for Christmas celebrations. An alternative to using traditional, large, fresh-cut or potted Christmas trees could be forcing these evergreen species in a small (≈1-L) container that could be displayed on a tabletop. We initiated this study to determine consumer preferences and marketability for six evergreen tree species produced for tabletop display and used three decoration themes and three price points. We constructed a web-based survey in which 331 participants were compensated with a $5 e-coupon for viewing 27 photographs of tabletop trees and providing preference and use information. The conjoint model accounted for 91.2% of the variance and showed that consumers valued tree species as the most important attribute (61% of the tree value), with decoration color/theme the second most important feature (27%) and, last, price (12%). Black Hills spruce (Picea glauca var. densata (Moench) Voss) was the most preferred species overall, and red was the most preferred decoration theme. Logically, the lowest price point was the most preferred. However, price was the most important attribute for participants younger than 25 years. The importance of price decreased as participant age increased until age 60, when price became a more important component. With a cost of production of $5.45 and decoration and shipping estimated at an additional $4.00, the product could be a profit generator priced at any of the tested price points ($14.95 and above).
Douglas B. Walsh, Frank G. Zalom, Douglas V. Shaw, and Kirk D. Larson
Forty-eight strawberry (Fragaria ×ananassa Duchesne) or (Fragaria L. sp.) genotypes from the University of California advanced-cycle breeding population were evaluated over 7 years for susceptibility to and tolerance of infestation by two-spotted spider mite (Tetranychus urticae Koch). In pairwise tests, 23 photoperiodically short-day genotypes were compared with the short-day cultivar Chandler, and 23 day-neutral genotypes to the day-neutral cultivar Selva. Feeding by T. urticae resulted in substantial yield reductions regardless of genotype. Yield reduction from feeding by T. urticae averaged 29.9% for short-day and 23% for day-neutral genotypes. Calculation of variance components for day-neutral genotypes determined that none of the variation in yield was explained by the interaction of genotype and T. urticae infestation, whereas 24.4% of the variation in yield for short-day genotypes was explained by the interaction of genotype and T. urticae infestation. Under current strawberry production practices in California there appears to be little potential for breeding direct resistance to T. urticae for day-neutral genotypes. However, some gains in breeding direct T. urticae resistance may be achieved within short-day genotypes. Phenotypic path-coefficient analysis for direct and indirect effects, and simple correlation coefficients of T. urticae feeding determined there were substantial differences between short-day and day-neutral genotypes in their yield responses to T. urticae feeding. For short-day genotypes, the greatest direct effect on yield resulted from T. urticae feeding in June. For day-neutral genotypes, the greatest direct effects resulted from T. urticae feeding in April and May and were probably due to the day-neutral genotype's more complex flowering responses. Several high-yielding cultivars have been developed and released over the 7 years of this study. It appears the new cultivars that were bred for current cultural practices exhibited a consistent plant response for greater yield both in the presence and absence of T. urticae feeding.
Nnadozie C. Oraguzie, Sue E. Gardiner, Heather C.M. Basset, Mirko Stefanati, Rod D. Ball, Vincent G.M. Bus, and Allan G. White
Four subsets of apple (Malus Mill.) germplasm representing modern and old cultivars from the repository and apple genetics population of the Horticulture and Food Research Institute of New Zealand Limited were used in this study. A total of 155 genotypes randomly chosen from the four subsets were analyzed for random amplified polymorphic DNA (RAPD) variation. Nine decamer primers generated a total of 43 fragments, 42 of which were polymorphic across the 155 genotypes. Pairwise distances were calculated between germplasm subsets using the distance metric algorithm in S-PLUS, and used to examine intra-and inter-subset variance components by analysis of molecular variation (AMOVAR). A phenogram based on unweighted pair group method with arithmetic average (UPGMA) cluster analysis was constructed from the pairwise distances and a scatter plot was generated from principal coordinate analysis. The AMOVAR showed that most of the variation in the germplasm (94.6%) was found within subsets, suggesting that there is significant variation among the germplasm. The grouping of genotypes based on the phenogram and scatter plot generally did not reflect the pedigree or provenance of the genotypes. It is possible that more RAPD markers are needed for determining genetic relationships in apple germplasm. Nevertheless, the variation observed in the study suggests that the current practice of sublining populations in the first generation to control inbreeding may not be necessary in subsequent generations. If these results are confirmed by fully informative molecular markers, germplasm managers should reassess the structure of their genetics populations. There may be a need to combine sublines in order to capture the maximum genetic diversity available and to streamline breeding efforts.
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.
Byron L. Frenz and Jack E. Staub
Development projects in developing countries are generally considered to be speculative investments. Potentially significant returns on investment opportunities are often overlooked by assuming that investment risks in developing countries are greater or less manageable than the risks of investment in developed countries. An import purchasing-risk evaluation identified the costs associated with the production and export of processing cucumbers (Cucumis sativus L.) from Hispaniola (Haiti and the Dominican Republic) to the United States. Although production and export analyses suggested that Hispaniola might not replace Mexico as the primary source of cucumbers for processing in the United States between November and April, Hispaniola affords the U.S. processing industry with an alternative investment option for reducing single-sourcing raw product risk. Therefore, an import diversification evaluation was conducted using Monte Carlo simulation to define a investment-risk model. Monte Carlo simulations of the means and variances of the components of cost andprice were used to assess investment risk under various investment strategies. This model identified sources of cost variation which were then used to characterize export risks derived from growing processing cucumbers on Hispaniola. It was determined that U.S. processors can reduce overall purchasing-risk by diversifying Mexican production to Hispaniola. Through the creation of a strategic transportation alliance between the U.S. and Hispaniola project participants, the export-import costs were such that the investment-risk model identified the allocation of 80% of the production in Mexico and 20% in Haiti as the most favorable diversification strategy. This strategy offered less risk and greater potential long-term returns than purchasing cucumbers solely in Mexico.
In the article, Heritability and Genetic Variance Components Associated with Citrulline, Arginine and Lycopene Content in Diverse Watermelon Cultigens by Wehner et al. [HortScience 52(7):936–940 doi: 10.21273/HORTSCI11255-16], there was a mistake in
Flower buds of two sweet cherry (Prunus avium L.), 12 sour cherry (Prunus cerasus L.) and one ground cherry (P. fruticosa Pall.) were collected monthly from Aug. 1990 to Mar. 1991, and subjected to freeze tests to determine the level of cold hardiness. LT50 values (temperatures at which 50% of the flower buds were killed) summed over all months were significantly correlated (r = 0.6844, P ≤ 0.01) to the flower bud low temperature exotherms (LTEs). Correlation of LTEs to LT50 values was highest, r = 0.85, P ≤ 0.01 for the acclimation and midwinter period, November to February collections. During this period the average LT50 occurred before and within 2.5 °C of the LTE, indicating tissue injury before the LTE occurrence. During deacclimation, represented by the March collection, the LT50 began within 2.0 °C, on average, of the LTE, and in 11 of 12 cultivars and seedlings preceded the LTE. In March, the correlation of LTEs to LT50 values was less, r = 0.69, P ≤ 0.05, indicating possible changes flower bud deep supercooling. LTE values were selected as a measure of flower bud hardiness in sour cherry. Exotherms were not detected in the flower buds of all germplasm tested on all evaluation dates, but were the best means of separating selections. While LTE analyses expressed significant differences in November, December, and March at P ≤ 0.01, the LT50 analyses expressed differences only in December and February at P ≤ 0.05. The relationship between ambient temperatures and floral tissue hardiness indicated that November and March are two critical times for flower bud injury. November injury would occur in years when sudden low temperatures occur without sufficient pre-exposure to freezing temperatures. March injury would occur in years when sudden freezing temperatures follow warm days. This type of injury would be most pronounced in southern genotypes. Spring freeze injury could be significantly reduced by the selection of cultivars and seedlings that have delayed deacclimation. Exotherm occurrence and bud volume were correlated (r = 0.95, P ≤ 0.05). In January, when exotherms were least prevalent, they were generally present only in the five cultivars and seedlings with large bud volumes. The LTEs in midwinter, occurred within 3 °C of the reported average annual minimum temperature for the northern range of Prunus commercial production (Zone 6). The results of the principal component analysis of flower bud LTEs indicated that other selection criteria as flowering time might have played a more significant role in the hardiness range of sour cherry than simply geographic origin. The first principal component (PC1), which accounted for 77% of the total variance was used to separate among cultivars and seedlings. Selections at the positive end of PC1 had flower buds that were more cold susceptible than selections at the negative end of PC. This concurs with other research showing that flower bud hardiness is related more to commercial range (i.e., the range of commercial production) than to geographic distribution.
J. Steven Brown, Raymond J. Schnell, Tomás Ayala-Silva, J. Michael Moore, Cecile L. Tondo, and Michael C. Winterstein
following transformations (or no transformation) for a totally random ANOVA to estimate variance components by maximum likelihood: fruit weight = natural log; fruit length = no transformation; fruit width = natural log; anthracnose resistance = no