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John A. Juvik, Gad G. Yousef, Tae-Ho Han, Yaacov Tadmor, Fermin Azanza, William F. Tracy, Avri Barzur, and Torbert R. Rocheford

This study was conducted to identify the chromosomal location and magnitude of effect of quantitative trait loci (QTL) controlling sweet corn (Zea mays L.) stand establishment and investigate the impact of dry kernel characteristics on seedling emergence under field conditions. Genetic and chemical analysis was performed on two F2:3 populations (one homozygous for su1 and segregating for se1, the other homozygous for sh2 endosperm carbohydrate mutations) derived from crosses between parental inbreds that differed in field emergence and kernel chemical composition. A series of restriction fragment-length polymorphism (RFLP) and phenotypic markers distributed throughout the sweet corn genome were used to construct a genetic linkage map for each population. F2:3 families from the two populations were evaluated for seedling emergence and growth rate at four locations. Mature dry kernels of each family were assayed for kernel chemical and physiological parameters. Composite interval analysis revealed significant QTL associations with emergence and kernel chemical and physiological variables. Improved emergence was positively correlated with lower seed leachate conductivity, greater embryo dry weight, and higher kernel starch content. QTL affecting both field emergence and kernel characteristics were detected in both populations. In the su1 se1 population genomic regions significantly influencing emergence across all four environments were found associated with the se1 gene on chromosome 2 and the RFLP loci php200020 on chromosome 7 and umc160 on chromosome 8. In the sh2 population the RFLP loci umc131 on chromosome 2 and bnl9.08 on chromosome 8 were linked to QTL significantly affecting emergence. Since seedling emergence and kernel sugar content have been shown to be negatively correlated, undesirable effects on sweet corn eating quality associated with each emergence QTL is discussed. Segregating QTL linked to RFLP loci in these populations that exert significant effects on the studied traits are candidates for molecular marker-assisted selection to improve sweet corn seed quality.

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Daniela Farinelli, Pierluigi Pierantozzi, and Assunta Maria Palese

The effect of several pollination combinations of the olive cultivars Ascolana Tenera, Carolea, Leccino, and Picholine on seed quality and seed number and drupe and seed features were evaluated in 2007 and in 2008 in central Italy. The well-known pattern in olive fruit was confirmed by the high percentage of drupes (71.8%, on average) containing one seed with a closed endocarp, as the dispersal unit, optimizing the plant’s investment in seedling survival. Based on the results of the χ2 test of independence, there was a significant maternal and paternal effect on the number of normal seeds per drupe in some years and combinations. Particularly, in 2007, Picholine and Leccino cultivars (as mother) had drupes with two normal seeds (23.7% and 3.1%, respectively, with respect to 10.8% observed in a normal seed pattern), confirming that double-seeding in olive could be cultivar-dependent. Also the specific crosspollination between ‘Carolea’, as a pollenizer, and ‘Ascolana Tenera’ gave rise to a higher proportion of double-seeded drupes in 2007 (39% with respect to 14.3% expected to be in this category). In 2008, although ‘Ascolana Tenera’ produced more drupes with undeveloped seeds (31.9% with respect to 19.7% expected to be in that category), ‘Leccino’ and ‘Carolea’ had drupes with a lower number of undeveloped seed (14.2% and 11.5%, respectively). ‘Maurino’ and ‘Ascolana Tenera’ pollen produced significant effects on ‘Leccino’ drupes by increasing the number of drupes with undeveloped seeds in both experimental years. Double-seeded drupes outweighed those with only one normal seed in ‘Leccino’ and ‘Picholine’. Instead, drupes with undeveloped seeds affected fruit weight, being generally lighter than those with normal seeds. Although the Leccino cultivar, combined with ‘Maurino’ and ‘Ascolana Tenera’, greatly increased the proportion of drupes without normal seed, such condition did not affect their final weight, which was not different from those with one normal seed, suggesting that this variety caused late seed death.

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Haim Nerson

Field experiments were conducted in 1996 and 1997 to examine the effects of plant density on yield and quality of fruit and seeds of muskmelons (Cucumis melo L.). Two open-pollinated cultivars, Noy Yizre'el (Ha'Ogen type) and TopMark (western U.S. shipper type), were grown at plant densities ranging from 0.5 to 16.0 plants/m2 under commercial conditions. The highest marketable fruit yields were achieved with plant densities of 2 to 4 plants/m2. In contrast, the highest seed yields were obtained at 8 to 12 plants/m2. Seed yield index [seed yield (g)/fruit yield (kg)] was used as a parameter to define seed production efficiency. High seed yield was closely related to high value of the seed yield index. High seed yield indexes resulted from high plant densities (up to 12 plants/m2), at which the crops produced many, but relatively small fruit. In all cases, the seed yield per fruit (seed number and seed size) increased with increasing fruit weight. However, the sum of the seed yield of two small fruit was always greater than the seed yield of one, double-sized fruit. There was a clear exception with extremely small fruit (<500 g), which produced both low seed yields and poor seed quality. A positive relationship was found between fruit size and seed size in both cultivars. Nevertheless, relatively small seeds (25 to 30 mg) extracted from relatively small fruit (500 to 1000 g) showed the best performance in terms of germination and emergence percentages and rates, and in the vegetative development vigor of the seedlings.

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Gunching Siriwitayawan, A. Bruce Downie, and Robert L. Geneve

Sweet corn (Zea mays L.) and tomato (Lycopersicon esculentum Mill.) seeds were aged naturally for 18 months or artificially aged using saturated salt accelerated aging to provide seed lots that differed in seed vigor, but retained a high standard germination percentage. Seed vigor was confirmed using standard vigor tests, including time to radicle emergence, cold, and accelerated aging tests. Ethylene evolution from both sweet corn and tomato seeds during germination was positively correlated with seed quality. Differences in ethylene evolution between nonaged and aged seeds were greater in seeds germinated on exogenous 1-aminocyclopropane-1-carboxylic acid (ACC). After 36 hours, there was about a 15-fold increase in ethylene evolution from seeds treated with 5 mm ACC compared to untreated seeds. Naturally and artificially aged seeds responded similarly and showed reduced ethylene production compared to nonaged seeds. In contrast to ethylene production, endogenous ACC titers were less for nonaged compared to aged seeds. Exogenous application of ACC to artificially aged seeds reduced the time to radicle protrusion, but did not completely reverse age-related effects on vigor. The data indicate that the reduced ability to produce ethylene in aged seeds was related to ACC oxidase (ACCO) synthesis or activity. Using Northern blot analysis, ACCO mRNA was detected after 48 hours of imbibition in nonaged seeds, but was undetectable in aged seeds affirming the contention that ACCO synthesis was delayed or reduced by aging. The current study provides additional support for ethylene as a biochemical indicator of seed vigor in seed lots with reduced vigor but high germination capacity.

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C. Yang, D.Y. Jiao, Z.Q. Cai, H.D. Gong, and G.Y. Li

Plukenetia volubilis Linneo, a tropical recurrent woody oilseed plant native to South America, was successfully introduced in China. A field experiment was conducted to determine the effect of the dry-season foliar sprays once every 2 weeks with 50 μm water or five different plant growth regulators (PGRs) viz., gibberellic acid (GA3), kinetin (KIN), indole-3-acetic acid (IAA), abscisic acid (ABA), and salicylic acid (SA) on the growth and yield of P. volubilis plants in Xishuangbanna, southwest China. Results showed that PGRs affected the leaf stomatal conductance (g S) and water-use efficiency (WUEi), rather than the net photosynthetic rate (PN). The phenological development of P. volubilis plants, including the time of flowering and maturity, and the dynamic pattern of fruit ripening, was not altered by PGR treatments. ABA and SA resulted in highest fruit set, seed oil content, and total fruit or seed oil yield, whereas GA3, IAA, and KIN were effective in increasing seed size. The nonstructural carbohydrates (NSC) are related to subsequent abscission or retention of the developing fruit, which was indicated by the positive relationship between carbohydrate concentration and fruit set across PGR treatments. The positive influences of PGRs on the total fruit yield (increased 4.3% to 15.2%) and total seed oil yield (increased 4.9% to 24.9%) per unit area throughout a growing season were found when compared with the control, depending to a great extent on the balance between vegetative and reproductive growth during the reproductive stage. This study suggests that PGRs, especially for ABA and SA, can become a valuable tool for promoting the seed oil yield of P. volubilis plants while maintaining high seed quality in the field.

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J. Blasiak, A. Kuang, C.S. Farhangi, and M.E. Musgrave

Seeds developing within a locular space inside hollow fruit experience chronic exposure to a unique gaseous environment. Using two pepper cultivars, `Triton' (sweet) and `PI 140367' (hot), we investigated how the development of seeds is affected by the gases surrounding them. The atmospheric composition of the seed environment was characterized during development by analysis of samples withdrawn from the fruit locule with a gas-tight syringe. As seed weight plateaued during development, the seed environment reached its lowest O2 concentration (19%) and highest CO2 concentration (3%). We experimentally manipulated the seed environment by passing different humidified gas mixtures through the fruit locule at a rate of 60 to 90 mL·min-1. A synthetic atmosphere containing 3% CO2, 21% O2, and 76% N2 was used to represent a standard seed environment. Seeds developing inside locules supplied with this mixture had enhanced average seed weight, characterized by lower variation than in the no-flow controls due to fewer low-weight seeds. The importance of O2 in the seed microenvironment was demonstrated by reduction in seed weight when the synthetic atmosphere contained only 15% O2 and by complete arrest of embryo development when O2 was omitted from the seed atmosphere. Removal of CO2 from the synthetic atmosphere had no effect on seed weight, however, the CO2-free treatment accelerated fruit ripening by 4 days in the hot pepper. In the sweet peppers, fruit wall starch and sucrose were reduced by the CO2-free treatment. The results demonstrate that accretionary seed growth is being limited in pepper by O2 availability and suggest that variation in seed quality is attributable to localized limitations in O2 supply.

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Matthew D. Kleinhenz

programs and international working groups.” “Mark explained relationships among seed quality, stand establishment, and system productivity and helped steer improvements in all through independent and collaborative efforts. Mark bridged research, real

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Samuel Contreras, Mark A. Bennett, and David Tay

of seed quality such as germination, germinability, and storability. In general, the consensus is that water deficiency during seed development reduces dormancy and improves germination of wild species ( Fenner, 1991 ; Gutterman, 2000 ; Hilhorst and

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Warley M. Nascimento, Jairo V. Vieira, Giovani O. Silva, Kathleen R. Reitsma, and Daniel J. Cantliffe

genetic effects, although the mother-plant environment during seed development and maturation can also affect carrot seed quality ( Gray et al., 1988 ) and influence thermotolerance as observed in other species ( Sung et al., 1998 ). Also, tolerance to

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Isabel Pimentel and Samuel Contreras

Lettuce, one of the most important vegetable crops in the world, is established through direct sowing or the transplant of seedlings; in both cases, high seed quality is essential to achieve a successful crop as low or slow germination results in