Callose depositions underlie the incompatible reaction in intergeneric crosses of rice

Distant hybridization of cereals is often impaired by fertilization barriers. Haploid induction through intergeneric crossing is well developed in wheat but has not been successful in rice due to incompatibility issues. The present study was thus undertaken to identify fertilization barriers that hinder the compatibility of the rice cultivar Punjab Rice 121 with maize and pearl millet lines as pollinators. A total of 37,357 spikelets were pollinated, yielding 494 caryopses upon supplementation with auxins. The resultant caryopses, arising from true intergeneric crosses, lacked embryos. Imaging of the pollinated pistils at different intervals indicated that intense callose depositions block the release of generative nuclei to the ovule in these wide crosses. Rice spikelets pollinated with rice pollen (cis-generic crosses) exhibited positive indicators of fertilization reaction at the micropyle. While the cis-generic crosses initiated true caryopsis formation after 24 h, no comparative reaction was observed in the intergeneric crosses. The current survey underlines that the rice female gametophyte presents a strong pre-fertilization barrier to foreign pollen. This barrier may be modulated in the future by altering genotype and auxin combinations.

An Analysis of Pollen Parameters, Fruit Set and Fruit Development During Attempts on Intergeneric Hybridization of Papaya (Carica papaya L.)

Research was conducted at the University Orchard, Horticultural College and Research Institute, to investigate the extent of pollen production, pollen fertility, fruit set, fruit growth and seed set as well as seedling vigour when two wild relatives of papaya (Vasconcellea cauliflora and Vasconcellea candamarcensis) are involved in the hybridization programme as male parents with three papaya cultivars (CO 7, TNAU Papaya CO 8 and Pusa Nanha) as female parents. Among the two wild relatives, V. candamarcensis was more polleniferous but with significantly lesser pollen viability and germination than V. cauliflora. Among the six intergeneric crosses, although the fruit set ranged from 60.00% to 93.33% the fruit retention till harvest was only 30.77 per cent to 35.71 per cent. The study also revealed metaxenic influence of wild parent on the growth of the fruits derived after crossing. Seed set was observed only with CO 7 as female parent but the seed size and weight, germination and seedling vigour recorded by intergeneric crosses of CO 7 with Vasconcellea were found to be low. The implications of the observations are discussed in relevance to employing the wild relatives for improvement of papaya.

Interspecific and Intergeneric Hybridization in Baptisia and Thermopsis

Interspecific and intergeneric crosses were performed between species in the genera Baptisia and Thermopsis with the goal of creating hybrids with the best qualities of both parents. Baptisia australis (L.) R. Br. was used as both the male and female parent in intergeneric crosses. Thermopsis chinensis Benth. ex S. Moore, T. lupinoides (L.) Link, and T. villosa Fernald & B.G. Schub. were used as male and female parents in both interspecific and intergeneric crosses. Pollen was collected from B. alba (L.) Vent., B. bracteata Muhl. ex Elliott, and B. lanceolata (Walt.) Ell. and used to make interspecific and intergeneric crosses. Putative hybrids were obtained from both interspecific and intergeneric crosses. Interspecific crosses produced a higher percentage of pollinations resulting in seed set and the number of seeds per pollination than intergeneric crosses. Morphological differences between parent species and progeny were evident in putative hybrids resulting from intergeneric crosses between T. villosa and B. australis and T. villosa and B. alba. Most putative hybrids bloomed during the second year after germination. Because seedlings could be obtained from both interspecific and intergeneric crosses, hybrids within and between the genera Baptisia and Thermopsis are feasible. The Fabaceae family contains 670–750 genera and 18,000–19,000 species. Baptisia (commonly called false or wild indigo) and Thermopsis (commonly named false lupine) of the Fabaceae belong to the tribe Thermopsidae, which comprises 46 species in six genera. All species in Thermopsis and Baptisia are herbaceous; they are the only two genera in Thermopsidae that do not have woody species. Thermopsis contains 23 species and has a wide-spread distribution with species endemic to Asia and much of temperate North America. Although Thermopsis is considered to have originated in central Asia, T. chinensis Benth. ex S. Moore and T. fabacea (Pallas) Candole are thought to have originated in North America and migrated over the Bering Land Strait to Asia. Three Thermopsis species, T. fraxinifolia Nutt. ex M.A. Curtis, T. mollis (Michx.) M.A. Curtis ex A. Gray, and T. villosa Fernald & B.G. Schub., are native to the southeastern United States. Baptisia contains 15–17 species that are endemic to the southeastern and midwestern United States.

Interspecific and Intergeneric Hybridization in Dissotis and Tibouchina

Four species of Dissotis and three species of Tibouchina, two genera of the Melastomataceae family, were crossed in an attempt to create interspecific and intergeneric hybrids. Intergeneric crosses set seed at a rate of 18.1% and interspecific crosses had a 32.3% rate of seed set. Germination was extremely poor, with only four crosses having germinated seed. Crosses produced 31 seedlings. Three of the seedlings were from intergeneric crosses between Dissotis canescens and Tibouchina lepidota. Interspecific crosses produced 25 seedlings from crosses between Dissotis princeps and Dissotis rotundifolia and three seedlings from crosses between D. canescens and D. princeps. The prognosis for conventional breeding for species in Dissotis and Tibouchina is poor due to low seed set, poor germination, and slow growth of progeny.