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Mark E. Herrington, Craig Hardner, Malcolm Wegener, Louella L. Woolcock, and Mark J. Dieters

risk and severity of these losses. The studies reported here estimate the genetic control (i.e., heritability) of resistance to rain damage, particularly damage resulting from water soaking and surface etching because initial observations indicated that

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Christopher S. Cramer*

Heritability estimates of bolting percentage (BP), pink root (PR) and Fusarium basal rot (FBR) incidences, and percentage of single centered (PSC) bulbs were calculated for an intermediate-day, open-pollinated onion population using selection response and half-sib (HS) family analyses. BP was determined by counting the number of seedstalks per plot when the population was seeded at an earlier planting date to induce bolting. PR and FBR incidences were determined by rating 30 bulbs/plot for the severity of PR and FBR, and calculated an incidence rate from the number of infected bulbs out of 30 rated. The PSC bulbs was determined by cutting transversely 30 bulbs at the vertical center of the bulb and looking for the presence of a single growing point or multiple growing points within 1.3 cm from the center of the bulb. Families were also evaluated for bulb quality that consisted of shape, size, maturity, firmness, number of scale layers, and dry outer scale thickness, adherence, retention, and color. Families were selected based upon an index that equally weighted BP, PR and FBR incidences, PSC bulbs, and bulb quality. No progress was made for BP even though the narrow sense heritability (h2) estimate was 0.51. PR and FBR incidence was reduced by 18% and 12%, respectively, and realized heritability (RH) estimates of 0.65 and 0.60, respectively, were calculated. h2 estimates calculated through HS family analysis was 0.46 and 0.37, respectively, for these two traits. Very little progress was made for the PSC bulbs and this was reflected in a RH estimate of 0.17. However, the h2 estimate was 0.71, suggesting that progress should be possible.

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W. R. Maluf, S. M. Azevedo, and V.P. Campos

Heritabilities for resistance to root knot nematodes (Meloidogyne javanica and Meloidogyne incognita races 1, 2, 3, and 4) were studied in a population of 226 sweetpotato clones of diverse origin. For each nematode isolate tested, 128-cell speedling trays were filled with previously inoculated substrate (30000 eggs/1000 mL substrate). Sweetpotato clones suitably tagged and identified were randomly planted in the cells (one plant/cell), with a total of four plants per clone per isolate. Ninety days after inoculation, sweetpotato plants had their roots washed for substrate removal, and treated with 150 mg·L–1 Phloxine B to stain nematode egg masses. The number of egg masses per root was recorded, and plants were accordingly assigned scores from 0 (highly resistant) to 5 (highly susceptible). Broad-sense heritability estimates were 0.87, 0.91, 0.81, 0.95, and 0.93 respectively for resistance to M. javanica and races 1, 2, 3, and 4 of M. incognita. The frequencies of resistant genotypes were higher for M. javanica and lower for M. incognita race 2. Genotypic correlations (rG) among the resistances to the various Meloidogyne isolates utilized were weak, ranging from 0.11 to 0.57, suggesting independent genetic controls. Clones could be selected, however, with high levels of resistance to all nematode isolates tested. (This work was supported by CNPq, CAPES, FAPEMIG, and FAEPE/UFLA.)

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Shuyin Liang, Xuan Wu, and David Byrne

stage much earlier ( Gitonga et al., 2014 ). With diploid roses, a heat shock treatment (1 h at 44 °C) decreased flower diameter (15.7%), petal number (23.3%), and flower dry weight (16.9%). A genetic analysis indicated that flower size is heritable

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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.

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Omar Carrillo-Mendoza, José X. Chaparro, and Jeffrey Williamson

hybrids of this cultivar tended to express this growth habit, showing that it is heritable and has a propensity toward dominance of this trait. Analysis of peach × almond F 1 s backcrossed to almond indicated that tree size was larger than peach and the

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Michelle L. Paynter, Joanne De Faveri, and Mark E. Herrington

strawberry cultivars has also been observed by Hutton and Gomez (2006) . Information about the heritability of the resistance in strawberry and estimation of the breeding value of individual plants would be beneficial in identifying highly resistant

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Javier Obando, Juan Pablo Fernández-Trujillo, Juan Antonio Martínez, Antonio Luis Alarcón, Iban Eduardo, Pere Arús, and Antonio José Monforte

the same NIL and one of PS at random. The judges determined whether at least one sample from the three presented differed from the other two. Statistical analysis. The statistical analysis and the estimation of the narrow-sense heritability ( h

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Daniel J. Bell, Lisa J. Rowland, John Stommel, and Frank A. Drummond

their inclusion can inflate variance estimates and possibly underestimate the GCA/SCA ratios and, thus, heritability estimates ( Shattuck et al., 1993 ; Wright, 1985 ). Also, because transformed data can cause distortions of the GCA/SCA ratios, we did

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Rolland Agaba, Phinehas Tukamuhabwa, Patrick Rubaihayo, Silver Tumwegamire, Andrew Ssenyonjo, Robert O.M. Mwanga, Jean Ndirigwe, and Wolfgang J. Grüneberg

variability in a given population ( Abinasa et al., 2011 ). The objective of this study was to estimate genotypic means, variance components, broad sense heritability, GCV, PCV, and correlations for yield components [i.e., SRFY, SRDY, VNY, FBY, and harvest