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Timothy F. Wenslaff and Paul M. Lyrene

A study was done to test whether inheritance is tetrasomic or disomic in tetraploid Fl hybrids between 2x Vaccinium elliottii Chapm. and 4x V. corymbosum L. Seventeen Fl hybrids derived from V. elliottii homozygous for recessive anthocyanin deficiency (AD) were confirmed by isozyme analysis and, where V. elliottii was the seed parent, by the presence of anthocyanin. Fertile hybrids with high pollen stainability were assumed to be 4x and duplex for the AD allele, having arisen from 2n gametes in V. elliottii. In nine Fl × Fl crosses, all progeny populations segregated for AD phenotype at or above the expected tetrasomic ratio of 1 AD:35 normal; no AD would be expected with disomic inheritance. Tetraploid AD progeny were used in testcrosses on sixteen Fl hybrids in 1991. Progeny segregated tetrasomically, 1 AD:5 normal. Isozyme loci PGD-2 and PGI-2 also segregated tetrasomically.

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Timothy F. Wenslaff and Paul M. Lyrene

Two diploid yellowleaf Vaccinium elliottii Chapmn. clones were pollinated with pollen from the tetraploid southern highbush cultivar `Misty' (largely V. corymbosum L). These interspecific crosses, which normally yield few hybrids because of a triploid block, were made with and without the use of V. elliottii mentor pollen mixed with V. corymbosum pollen. Mentoring had no effect on the number of hybrids produced when V. elliottii `Silverhill' was the seed parent, but when V. elliottii `Oleno' was the seed parent, no hybrids were produced unless mentor pollen was utilized. The difference was postulated to be a greater ability to produce one-seeded berries in `Silverhill' than in `Oleno'.

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Timothy F. Wenslaff and Paul M. Lyrene

Two clones of anthocyanin-deficient (AD) Vaccinium elliottii (2×, homozygous recessive, yy) were used as seed parents in experiments combining normal and AD pollen. AD gives a seedling marker to distinguish the pollen parent. In the first experiment, flowers were pollinated daily for one, two, three or four days. AD and normal V. elliottii pollen were applied on separate days. The last day of each treatment received the opposite genotype from the previous day(s). The first pollination gave as many, or more, seedlings as later applications but the number of seeds per fruit was higher with multiple pollen applications. The second experiment used pollen from normal V. corymbosum (4×) alone or mixed with AD pollen from the 2× clones. Results depended on the seed-parent genotype. There was no difference between treatments in the number of hybrids produced by W81-1, which tends to set fruit even with only one seed per berry. Only mixed pollen yielded hybrids from clone FL83-139, which was never observed to produce berries with only one seed; apparently the mentor AD pollen helps to set the fruit, thereby allowing the rare hybrid seeds to develop.

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Richard M. Manshardt and Timothy F. Wenslaff

Abstract

A study of reproductive barriers limiting interspecific hybridization between Carica papaya L. and C. cauliflora Jacq. was undertaken in four reciprocal interspecific crosses using two different lines of each species. Particular attention was focused on determining whether polyembryonic clusters produced in these crosses were of maternal or zygotic origin. Prezygotic barriers were unimportant; pollen tube penetration and zygote formation were similar in intra- and interspecific crosses. Substantial postzygotic disruptions were observed, including disorganized growth and abortion of hybrid embryos and lack of normal endosperm development. In most crosses, disorganized embryos aborted before differentiating into polyembryonic structures. However, crosses employing UH345 (C. cauliflora) as female parent produced some embryos that developed to maturity (6 months), and, in these crosses, embryogenic proliferation from zygotic tissue became evident as early as the beginning of the 3rd month. There was no evidence of somatic embryogenesis from maternal tissues in any cross. Embryos rescued 3 to 6 months after pollination continued embryogenic growth in vitro on basal Murashige and Skoog (MS) medium and germinated on medium containing 0.2 mg BA/liter and 0.5 mg NAA/liter. Zymograms assayed for isocitrate dehydrogenase, malate dehydrogenase, and phosphoglucomutase activity confirmed the zygotic origin of tissues taken from in vitro cultures and recovered plantlets. Vigor, viability, and fertility (< 1% stainable pollen) of hybrids recovered from embryo culture were low. Chemical names used: 6-benzylaminopurine (BA); 1-napthaleneacetic acid (NAA).

Open access

Richard M. Manshardt and Timothy F. Wenslaff

Abstract

Interspecific hybridizations were attempted between papaya (Carica papaya L.) and six Carica taxa, including C. monoica Desf., C. parviflora (A. DC.) Solms, C. pubescens Lenne et Koch, C. quercifolia (St. Hil.) Hieron., stipulata Badillo, and C. × heilbornii Badillo nm. pentagona (Heilborn). Prezygotic barriers were minimal; pollen tubes of wild species freely penetrated into the seed cavity of papaya, and papaya pollen tubes were similarly unhindered in reciprocal pollinations on C. pubescens. Postzygotic barriers were formidable due to ovule abortion and endosperm failure. However, dissection of more than 150 C. papaya fruits 90 to 180 days after interspecific pollination yielded at least a few hybrid embryos of each species combination. All crosses in which C. papaya was the male parent failed, with the exception of C. pubescens × C. papaya, which succeeded only after young ovules were cultured 30 to 45 days after pollination. Multiple embryos were common in all successful crosses, and these were shown to be of zygotic origin by analyses of isocitrate dehydrogenase, malate dehydrogenase, and phosphoglucomutase isozymes in parental and hybrid tissues. Hybrids successfully recovered from in vitro cultures included C. papaya × C. pubescens and reciprocal, C. papaya × C. quercifolia, and C. papaya × C. stipulata.