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Mustafa M.A. Elballa and D.J. Cantliffe

The effect of temperature on seedstalk development, seed yield and quality in carrot (Daucus carota L.) was investigated in growth chambers at constant day/night temperatures of 33/28, 28/23, 25/20, 23/18, 20/15, and 17/12 °C. Days to flowering, seedstalk height, number of umbels, and seed yield decreased linearly with increasing temperature from 17/12 to 33/28 °C. Continuous high temperature (33/28 °C) had a detrimental effect on germination as measured by a standard germination test and an accelerated aging test. Optimum germination of the progeny occurred at 20/15 °C; however, germination rate was faster when seeds matured at 23/18 °C. Seeds that developed at 33/28 °C produced seedlings with the lowest vigor, while those which developed at 20/15 °C produced seedlings with the highest vigor. Brief exposure of plants to 33/28 °C during anthesis or early seed development was as detrimental to seed yield as continuous exposure to 33/28 °C. Exposure to high temperature (33/28 °C) during late seed development had less effect on seed yield, and seed quality was improved. Progeny vigor was reduced greatly by seed development at continuous high temperature (33/28 °C), but was unaffected by brief exposure to 33/28 °C at anthesis, early, or late in seed development. These results suggest that high (33/28 °C) day/night temperatures during pollination, fertilization, or early stages of seed development can greatly reduce carrot seed yield and seed quality.

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X.P. Zhang, B.B. Rhodes, W.V. Baird, W.C. Bridges, and H.T. Skorupska

This research was conducted to develop genic male-sterile lines of watermelon (Citrullus lanatus Matsum & Nakai) homozygous for the juvenile albino (ja) seedling marker. Male-sterile plants (msms) of the genic male-sterile line G17AB were crossed with a Dixielee plant that was heterozygous for the ja locus. Male-fertile, juvenile albino recombinants of the F2 progeny were self-pollinated, resulting in F3 progeny. The male-sterile normal green recombinants of the F2 progeny were crossed with an F1 hybrid plant with genotype MsmsJaja, and three populations (93JMSB-1, -2, and -3) were obtained from these crosses. Juvenile albino recombinants were confined to 93JMSB-1. Of the juvenile albino plants of 93JMSB-1, male-sterile plants were sib-crossed with male-fertile plants, resulting in 93JMSB-1-1. Progeny of 93JMSB-1-1 was homozygous for ja and segregated for ms in a 127 male-sterile: 128 male-fertile ratio, fitting a 1:1 ratio. The male-sterile juvenile albino plants of F3 were crossed with male-fertile juvenile albino plants of 93JMSB-1, resulting in 93JMSF3-1 and -2. Plants 93JMSF3-1 and -2 were homozygous for ja but segregated for ms at 10 male-sterile: 13 male-fertile and 15 male-sterile: 19 male-fertile for 93JMSF3-1 and 93JMSF3-2, respectively, fitting the 1:1 ratio. These three genic male-sterile lines with the ja seedling marker provide valuable germplasm for introducing ms and ja genes into diverse genetic backgrounds and for studying cross-pollination and gene flow in watermelon populations.

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X.P. Zhang, B.B. Rhodes, W.V. Baird, H.T. Skorupska, and W.C. Bridges

Juvenile albino, gene symbol ja, is a spontaneous virescent mutant, first observed in `Dixielee' and an F2 population of `G17AB' (msms) × `Dixielee' in 1992. Hypocotyls, new young leaves, shoot tips, tendrils and flowers on the main shoot of the ja mutant are all albino during early spring. The interior portions of albino leaves gradually become green, while the margins remain albino. Fruit rind color of the mutant is variegated. Growth of the ja mutant is severely impaired in the early spring. However, the mutant grows at a rate comparable to wild-type in the summer, and produces fruit of almost normal size. Genetic analysis of F1, F2, and BC1 populations derived from the ja mutant showed that the gene for the ja mutant is inherited as a single, recessive, nuclear gene. Segregation ratios in the F2 and BC1 progenies derived from the cross between the previously reported delayed green virescent mutant and the ja mutant indicate independent inheritance of the genes dg and ja. Temperature and red/far-red light had no differential effect on mutant and the wild-type plants. An increase of daylength from 8 to 15 hours increased fresh weight and chlorophyll content more in the ja mutant than in the wild-type. The mutant had a higher chlorophyll a: b ratio than the wild-type under long days. Chlorophyll synthesis or accumulation in the mutant is severely impaired under short days. This is the only virescent mutant in the family Cucurbitaceae whose expression is regulated by daylength.

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Branko R. Lovic and Donald L. Hopkins

While this article describes important steps to reduce the presence of potentially seedborne pathogens in seed production fields, information contained herein constitutes suggestions only and does not guarantee a disease-free crop. Despite

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Scott Neil White and Linshan Zhang

suppression in lowbush blueberry and reduce flowering tuft density, flowering tuft inflorescence number, and flowering tuft seed production and seed viability ( White and Kumar, 2017 ). However, efficacy is variable across sites and large tufts common in

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Alyssa H. Cho, Carlene A. Chase, Danielle D. Treadwell, Rosalie L. Koenig, John Bradley Morris, and Jose Pablo Morales-Payan

seed production. The hypothesis was that seeding rate and cutting to remove apical dominance would impact plant morphology, weed suppression, and seed production of sunn hemp. Materials and Methods The experiment was conducted on certified organic land

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Christopher J. D’Angelo and Irwin L. Goldman

longevity and sprout suppression, but can also delay growth when it is desired. Dormancy release, along with vernalization, are key processes for seed production during which rapid, uniform growth and development are valuable. There is great economic

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Kenneth W. Leonhardt

used to classify them as invasive is their seed production. High seed production compared with native species is one of the parameters that makes an introduced species invasive ( James et al., 2010 ). The success of many invasive trees is attributed to

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Christopher A. Clark, Tara P. Smith, Donald M. Ferrin, and Arthur Q. Villordon

plants as the cost for producing G2 plants is much lower than that for producing G1 seed, while the yield and quality remain relatively high. Although growers are encouraged to isolate their seed production from the rest of their commercial production, it

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Dale T. Lindgren and Daniel M. Schaaf

number of species in other taxonomic groups, there is a lack of uniformity between groups and within groups that precludes statistical comparisons for percent fruit set and average seed production. In total, 31 species in the subgenus Penstemon (≈182