Cross-pollination Rate Research Articles

Butterfly Visitors as Vectors of Ustilago violacea Spores between Caryophyllaceous Plants

Pollen and fungal spores on 104 butterflies were searched for under a scanning electron microscope. Evidence is presented that the fungus Ustilago violacea exploits a symbiotic system, i.e. plant-pollinator interrelation, to ensure an efficient and precise dispersal of its own spores. The host plant Viscaria vulgaris produces seeds, even if infected with Ustilago, indicating a rather harmless relationship since a higher rate of cross pollination may be achieved by fungus-infected plant individuals.

Rates of cross-pollination inLycopersicon pimpinellifolium: Impact of genetic variation in floral characters

Cross-pollination was tested between different genotypes ofLycopersicon pimpinellifolium in an experimental plot situated in the southerly range of the species. Rates of cross-pollination were found to be highly correlated with flower size and were related to a lesser extent with degree of stigma exsertion. Comparisons of fertility suggest that exsertion of 1.5 mm or more from the anther tube orifice interferes with automatic self-pollination, thereby increasing rates of cross-pollination. A single species ofExomalopsis (Anthophoridae), observed to visit all tested genotypes ofL. pimpinellifolium, was responsible for most of the pollination. Other species of solitary bees and other bee families participated in cross-pollination.

Polinização cruzada natural no feijoeiro

A fim de determinar a taxa de fecundação cruzada natural nas épocas em que o feijoeiro é cultivado em São Paulo, instalaram-se dois ensaios na Estação Experimental "Dr. Theodureto de Camargo", em Campinas. Usou-se o cultivar 'Chumbinho opaco', portador do fator genético recessivo que condiciona a côr branca das flôres, o qual foi plantado junto ao cultivar 'Mulatinho 1-208', portador do alelo dominante, para a côr violeta. Os dados obtidos permitiram concluir que a taxa de cruzamentos naturais foi da ordem de 1,26% na cultura "da sêca" e de 1,33% na "das águas". Essa taxa de cruzamentos naturais, embora de pequena grandeza, indica que nos campos de multiplicação de sementes, as linhagens devem ficar isoladas, a fim de se conservarem uniformes. Mostra, também, que pelo menos alguns dos atuais cultivares podem ter se originado como produto de recombinações, a partir de cruzamentos naturais.

POLLINATION RELATIONS OF LYCOPERSICON ESCULENTUM IN NATIVE AND FOREIGN REGIONS

Many of our important cultivated plants are cross-pollinated in their native habitat; when grown in other areas their pollination relations may present problems of general biological and practical significance. An unstable condition in foreign areas is anticipated since the flowers may be visited by alien pollen vectors or they may not be visited at all. Reproduction may be seriously affected in an obligatorily cross-pollinated plant-for example, alfalfa (Medicago sativa L.) growing in certain areas in California, where seed production seems to be limited by the fact that the flowers are not always visited by insect species that can adequately crosspollinate them (Linsley, 1946). Among plants commonly accepted to be completely self-pollinated, the garden pea (Pisum sativum L.) was recently found to be cross-pollinated to the extent of 3.3 per cent in Peru, a region that is outside the native habitat of this species (Harland, 1948). Again, differences as great as tenfold in rates of natural cross-pollination of the cultivated tomato (Lycopersicon esculenturn Mill.) were found in various localities in California (Rick, 1949). Such variations obviously have great bearing on breeding practices, methods of seed production, and even yields of the agricultural commodities themselves. Surprising variations are encountered even among anemophilous plants-for example, common wheat (Triticum1 vulgare Vill.), which is usually assumed to be highly self-pollinated. Rates of natural cross-pollination as high -as 34 per cent were found in the United States by Leighty and Taylor (1927), and a large number of natural hybrids between cultivated varieties were recognized by Howard et al. (1910) in the Punjab, where they observed that in the dry climate the glumes often opened, thereby exposing the stigmas to wind-borne pollen. The intrinsic pollination relations of a species are often assumed to be the same as those observed under cultivation in foreign areas. The examples of wheat and tomato just cited show how misleading such assumptions can be. The pollination relations, especially of facultatively cross-pollinated plants, in their native habitat can scarcely be predicted from information gained in foreign regions. Although the former relations may have important practical and theoretical bearing, extremely little is known about them. The tomato has been regarded as a highly self-pollinated plant, and until recently all published tests have indicated very low rates of natural cross-pollination in eight stations in the North Temperate Zone, all outside the range of distribution of the genus Lycopersicon (literature reviewed by Rick, 1949). On the other hand, two recently discovered facts hint that rates might be higher in the indigenous region; namely, rates vary greatly within and between localities in California; and L. peruvianum (L.) Mill.* and related species were found to be genetically self-incompatible and consequently dependent upon pollen vectors for their reproduction in nature (McGuire, unpublished). A study was therefore undertaken of the pollination mechanisms of wild and cultivated tomato species in the Andean region where the genus is native. The present report deals only with the study of L. esculentum and a

Genetics and development of nine male-sterile tomato mutants

Abstract does not appear. First page follows. Summary A search was conducted in commercial plantings of the San Marzano tomato for male-sterile mutants, potentially useful in producing F1 hybrid seed and in cross-breeding. Among 150 unfruitful plants, 12 were found to be genetically male-sterile. Breeding results indicate that the male sterility of each mutant is determined by a single recessive gene. One gene—ms5—was recovered four times. Eight other nonallelic genes—ms6 to ms13—were demonstrated. No mutants for female sterility or cytoplasmic male sterility were found. In the mutant ms5, 3 to 5 per cent of the microsporangia produced functional pollen; by using this pollen in self-pollination, pure-breeding male-sterile populations of ms5 were obtained. No functional pollen was produced by other mutants. The growth of anthers and, to a lesser extent, petals is suppressed to different degrees in the different mutants. The male-sterile segregates in some mutants can be identified macroscopically by the size and form of the floral parts, and in all of the mutants by the anther contents. Anthers are reduced most and breakdown of microsporogenesis occurs earliest in the four mutants whose petal length is significantly diminished. No effects of the genes were observed in other parts of the plant. The genes for male sterility exert their most profound effects on the pollen mother-cells and early microsporogenesis. The mutants differ in time and rate of breakdown. The behavior of chromosomes is normal until the time of breakdown and does not seem to account for failure of pollen development. Each gene affects tapetal development differently; in most mutants the breakdown is delayed, but in a few it occurs at the normal time or earlier. Pollen production is disrupted earliest in those mutants in which tapetal degeneration is delayed. Breakdown of microsporogenesis in ms5 involves an erratic orientation of sporogenous tissue, the latter usurping the locus of the outer tapetum and wall tissue. These effects are determined precisely and consistently, each preparation of a given mutant revealing the same pattern of breakdown. Counts of seed set after cross-pollination and examination of sectioned ovaries revealed no appreciable ovule sterility in any mutant except ms8. In the latter about 25 per cent of the ovules abort—not so many as to disqualify it as a pistillate parent for hybrid-seed production. The rates of natural cross-pollination of certain of the mutants differ with high statistical significance. The highest rate was observed in ms5, which is subject to a low rate of natural self-pollination. In the other eight mutants the rate of natural cross-pollination shows some positive correlation with size of anther tube, suggesting that the insect pollen vectors prefer to visit flowers whose form deviates least from normal. The best mutants for hybrid-seed production are those intermediate in anther abnormality—enough for easy macroscopic identification but not enough to reduce cross-pollination greatly.