Genetic diversity of arboreal cotton populations of the Brazilian semiarid: a remnant primary gene pool for cotton cultivars.

Mocó cotton belong to the same species as the cultivated species, Gossypium hirsutum, and cultivated forms were mainly landraces but also developed as cultivars, bearing good fiber quality and drought tolerant when cropped as a perennial species. The northeast Brazil crop system based on this cotton type is finished, with a few small area planted in the three main States, where it was previously cultivated (Ceará, Paraíba, and Rio Grande do Norte), but in others, maintenance is accomplished by single dooryard plants. Plants were found in all visited Northeast Brazil municipalities, sometimes in the North of the country, and were collected for ex situ preservation and evaluation. Most of seeds had no fuzz (62.2%) and 94.6% of the genotypes presented spot in flowers. Seventy-one alleles were revealed in 12 loci. The genetic structure of the population evaluated by microsatellite markers shows two main groups, one comprising the Seridó region where landraces were originated and other comprising the state of Ceará, where a specific breeding program was developed. Genotypes collected in North Brazil States as well as those collected in Bahia, Alagoas, and Sergipe grouped with those collected in Ceará. The Mantel correlogram indicates a significant (P < 0.05) correlation between genetic and geographical distances up to 77 km. The ex situ maintenance and agronomical evaluation are the main concerns for mocó, as the use of the agricultural interesting traits, possibly introgressed to other genotypes, is predicted. The in situ preservation is still of interest since there is more diversity there than in the collected plants and some should be continued due to use as medicinal plant.

Natural hybridization between Gossypium mustelinum and exotic allotetraploid cotton species.

Cotton has been collected in Brazil for decades for its conservation, evaluation, and the use of its genetic resources. Gossypium mustelinum is an allotetraploid cotton species that only occurs in Brazil, and little is known about its genetic potential for improvement. However, the species is threatened by habitat fragmentation and interspecific hybridization with exotic species of cotton. In this study, we investigated the rate of natural hybridization in two populations of G. mustelinum in Bahia, Brazil, with G. hirsutum and G. barbadense using a set of microsatellite markers.

Diversity and genetic structure among subpopulations of Gossypium mustelinum (Malvaceae).

Gossypium mustelinum is the only cotton species native to Brazil; it is endemic to the semi-arid region of the northeast. The populations are found near perennial and semi-perennial sources of water, such as ponds or pools in intermittent streams. Problems with in situ conservation derive from human interference in its habitat, mainly because of excessive cattle grazing and deforestation. Establishing efficient strategies for in situ conservation requires knowledge of the genetic structure of the populations. We evaluated the structure and genetic variability of populations of G. mustelinum in the Tocó and Capivara Rivers (State of Bahia). Two hundred and eighteen mature G. mustelinum plants were genotyped with SSR markers. The molecular data were used to estimate the allelic frequencies, the heterozygosity, the F statistics, and the genetic distance among the populations and among individuals. We found high genetic diversity among the populations. The FST indexes for each population were also high and strongly correlated with physical distance. The high estimated level of endogamy and the low observed heterozygosity are indicative that the populations reproduce mainly by self-fertilization and crosses between related individuals. Consequently, strategies for in situ preservation should include at least three occurrence sites of G. mustelinum from each population. For ex situ conservation, the collections should include as many sites as possible.

Molecular characterization of a virus from the family Luteoviridae associated with cotton blue disease.

Cotton blue disease is an aphid-transmitted cotton disease described in Brazil in 1962 as Vein Mosaic "var. Ribeirão Bonito". At present it causes economically important losses in cotton crops if control measures are not implemented. The observed symptoms and mode of transmission have prompted researchers to speculate that cotton blue disease could be attributed to a member of the family Luteoviridae, but there was no molecular evidence supporting this hypothesis. We have amplified part of the genome of a virus associated with this disease using degenerate primers for members of the family Luteoviridae. Sequence analysis of the entire capsid and a partial RdRp revealed a virus probably belonging to the genus Polerovirus. Based on our results we propose that cotton blue disease is associated with a virus with the putative name Cotton leafroll dwarf virus (CLRDV).

Occurrence, Distribution, and Relative Incidence of Five Viruses Infecting Cucurbits in the State of São Paulo, Brazil.

Cucurbits species grown in 38 of 40 agricultural regions in the state of São Paulo, Brazil, were surveyed for the relative incidence of Cucumber mosaic virus (CMV), Papaya ringspot virus-type W (PRSV-W), Watermelon mosaic virus-2 (WMV-2), Zucchini lethal chlorosis virus(ZLCV), and Zucchini yellow mosaic virus (ZYMV) during May 1997 and June 1999. Samples from 621 plants, representing eight cultivated species, six wild species, and one commercial hybrid (Cucurbita moschata × C. maxima), were analyzed by plate trapped antigen enzyme-linked immunosorbent assay (PTA-ELISA). PRSV-W and ZYMV were the most frequently found viruses, accounting for 49.1 and 24.8%, respectively, of 605 samples tested. ZLCV, CMV, and WMV-2 were detected in 7.8, 6.0, and 4.5% of 612, 497, and 423 samples tested, respectively. Double infection was found in 97 samples, and triple infection was found in 10 samples. Quadruple infection was detected in one C. pepo sample. Plants that were symptomatic but negative by PTA-ELISA might be due to abiotic agents, infection by virus for which antiserum was not available, such as Squash mosaic virus, or infection with an as yet uncharacterized virus.

Cayaponia tibiricae: New Host of Zucchini Yellow Mosaic Virus in Brazil.

Cayaponia tibiricae Cogn. (CT) is a wild Cucurbitaceae species found in secondary forests in the State of São Paulo, Brazil. The species has indefinite growth and bears oblong dark green fruits, 15 to 20 mm long (1,2). CT plants showing yellow mosaic symptoms were found in Atibaia County. Extracts from symptomatic plants were rub inoculated to zucchini squash (Cucurbita pepo L.) and Chenopodium amaranticolor Coste & Reyn. Zucchini squash plants developed severe yellow mosaic with intense leaf malformation, while C. amaranticolor showed necrotic local lesions. Extracts from naturally infected CT, zucchini squash, and C. amaranticolor were tested by plate trapped antigen-enzyme-linked immunosorbent assay (PTA-ELISA) with antisera against papaya ringspot virus type W (PRSV-W), zucchini yellow mosaic virus (ZYMV), zucchini lethal chlorosis virus (ZLCV), watermelon mosaic virus 2 (WMV-2), and cucumber mosaic virus (CMV). All samples were positive in PTA-ELISA only with ZYMV antiserum. Also, in Western blot (immunoblot) assay, ZYMV antiserum labeled a protein of approximately 36 kDa. Electron microscopic examination of ultrathin sections from infected CT tissue revealed the presence of pinwheel inclusions typical of potyvirus (type 1) infection in the cytoplasm of the cell. CT seedlings were susceptible to mechanical inoculation with the ZYMV isolated from this species. This is the first report of CT as a natural host for ZYMV in Brazil. References: (1) A. Cogniaux. Flora Brasiliensis 6:1, 1878. (2) M. Pio Corrêa. 1926. Diccionário das plantas úteis do Brasil e das exóticas cultivadas. Vol 1. Ministério da Agricultura, Rio de Janeiro, Brazil.