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  • Author or Editor: K. Baergen x
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Eight tomato (Lycopersicon esculentum Mill.) genotypes were evaluated based on shoot dry weight for resistance to four isolates of Verticillium dahliae Kleb. race 2 in two greenhouse seedling experiments. The race 2 isolates, obtained from North Carolina, Brazil, and Spain, demonstrated no differences in pathogenicity on the eight lines tested, thus precluding the identification of a third V. dahliae race in this collection. However, highly significant differences in virulence were observed among the isolates. The Brazilian isolate was the most virulent. No tomato genotype showed resistance comparable to that conferred by the single dominant Ve gene to V. dahliae race 1. While all tomato lines were susceptible to all race 2 isolates tested, there were significant differences in susceptibility equal to differences in levels of resistance. IRAT L3, Morden Lac, Okitsu Sozai, and `UC82' significantly outperformed the lowest ranking line XXIV-a. `Earlypak 7', Morden Mel, and Philippine 2 performance was statistically indistinguishable from that of either the highest- or lowest-ranked lines. Genetic diversity in the host and pathogen and environmental conditions favoring the pathogen likely contributed to the genotype × isolate interactions observed in Expt. 1. These results suggest using diverse isolates when screening for improved race 2 resistance.

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Seedlessness is an important breeding objective of most citrus scion improvement programs, but production of quality seedless triploid citrus via interploid crosses has historically been limited by the low quality of available tetraploid parents. Production of tetraploid hybrid parents from elite diploid scion cultivars via protoplast fusion is now a practical strategy, and numerous hybrids can be produced on a timely basis from a wide range of parents. Such hybrids can be used as pollen parents in interploid crosses to generate improved seedless triploid fresh fruit cultivars. Herein we report the production of 15 such hybrids from 17 different parents, including sweet orange [Citrus sinensis (L.) Osbeck], mandarin/tangerine (C. reticulata Blanco), grapefruit (C. paradisi Macf.), pummelo [C. grandis (L.) Osbeck], tangor (C. reticulata × C. sinensis), and tangelo (C. reticulata × C. paradisi) germplasm. All hybrids were confirmed by cytological and RAPD analyses, and have been budded to selected rootstocks to expedite flowering.

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