PERSPECTIVE: Pollen Cryopreservation for Plant Breeding and Genetic Resources Conservation.

Pollen conservation is an important tool for the maintenance of plant genetic resources and can promote improved efficiency in breeding programs and germplasm conservation and exchange. This review aims to understand the importance of pollen cryopreservation and how to use it for distinct species in order to encourage the use of this methodology in germplasm banks and plant breeding programs. Pollen from many plant species have already been successfully cryopreserved in liquid nitrogen. Analogous with other plant structures, to maintain pollen viability after storage at ultra-low temperatures it is necessary to adjust the water content so that at least the freezable is removed. Optimum pollen moisture levels for cryopreservation varies among species and different methods have been applied to control moisture content. Common methods to decrease pollen moisture content include exposure to saturated solutions of various salts (which have a well-defined relative humidity), silica gel, dry air or treatment with vitrification solutions. It is our understanding that pollen cryopreservation is a safe and practical alternative for conserving genetic material that is often neglected by potential users. The technique has the potential to overcome challenges of breeding programs, such as flowering asynchrony between different parent genotypes, and the production of insufficient pollen in nature. Generally, pollen cryopreservation techniques tend to be simple enough to be used routinely in research, plant breeding and germplasm conservation programs.

Morphological, cytogenetic, and molecular characterization of Arachis kuhlmannii Krapov. & W.C. Greg. (Leguminosae).

Arachis kuhlmannii occurs in Mato Grosso and Mato Grosso do Sul States, Brazil. Its area of occurrence partially overlaps with that of other species in the Arachis section. Because of their morphological similarities, these species are often mistaken one for another. This study aimed the correct classification of available accessions as Arachis kuhlmannii, or other species, and the characterization of similarities among accessions and Arachis hypogaea by morphological, cytogenetic, and molecular marker analyses. Thirty-eight accessions were used. Principal component analysis was used for morphological characterization, root tips for mitotic metaphase analysis, and RAPD markers for molecular characterization. Cluster analysis discriminated accessions with the A genome from the B genome. Cluster analysis based on molecular markers discriminated natural populations in a manner that correlated with geographical areas of the collection. Arachis cardenasii and A. hypogaea were isolated from other A-genome accessions. Cytogenetic analyses confirmed the existence of diagnostic characteristics that distinguish species with the A genome from those with the B genome. Results suggest the need for a taxonomic review of some species in the Arachis section, as we could not discriminate as distinct species all of the accessions identified as A. kuhlmannii, A. helodes, and A. simpsonii by using morphological, molecular, and cytogenetic markers.

Warm-Season (C4) Turfgrass Genotypes Resistant to Spittlebugs (Hemiptera: Cercopidae).

Screening for resistance to insect pests is one of the early stages of grass breeding programs. Pasture spittlebugs are sap-sucking insects that potentially cause severe damage to turfgrasses, including the loss of functional quality and perenniallity. The Brazilian flora has a large number of grass species with wide morphological variability and adaptability to different soil and climate conditions that can potentially be used as lawns. However, no study has screened turfgrass genotypes for resistance to spittlebug attack. In this study, we evaluated the intra- and interspecific variability of 35 turfgrass genotypes in the genera Paspalum, Axonopus, and Zoysia for resistance to the pasture spittlebugs, Deois flavopicta (Stal) and Notozulia entreriana (Berg) (Hemiptera: Cercopidae), as measured by damage scores, densities of nymphs and adults, and level of antibiosis resistance. Genotypes were grouped into three groups using cluster analysis and principal component analysis: GroupI had genotypes associated with low damage scores and high density of adult spittlebugs; GroupII had genotypes with intermediate damage scores and low density of nymphs and adults; and GroupIII was formed by genotypes with high damage scores and high nymph density. Intra- and interspecific genotypic variability was related to antibiosis resistance and morphological variation among genotypes with some indicating nonpreference resistance and others indicating tolerance resistance. Our results indicate that besides antibiosis resistance studies, it is essential to evaluate the morphological variability of grass genotypes when screening for resistance to insects. Further studies are needed to elucidate the intraspecific variability of Paspalum notatum Flüggé genotypes for resistance to spittlebug attack.

New hybrids from peanut (Arachis hypogaea L.) and synthetic amphidiploid crosses show promise in increasing pest and disease tolerance.

The primary gene pool of the cultivated peanut (Arachis hypogaea L., allotetraploid AABB) is very narrow for some important characteristics, such as resistance to pests and diseases. However, the Arachis wild diploid species, particularly those from the section Arachis, still have these characteristics. To improve peanut crops, genes from the wild species can be introgressed by backcrossing the hybrids with A. hypogaea. When diploid species whose genomes are similar to those of the cultivated peanut are crossed, sterile hybrids result. Artificially doubling the number of chromosomes of these hybrids results in fertile synthetic polyploids. The objectives of this study were: 1) to obtain progenies by crossing amphidiploids with the cultivated peanut, and 2) to characterize these two groups of materials (amphidiploids and progenies) so that they may be efficiently conserved and used. Using morphological, molecular, and pollen viability descriptors we evaluated one cultivar of A. hypogaea (IAC 503), eight synthetic amphidiploids, and the progenies resulting from four distinct combinations of crossing between IAC 503 and four amphidiploids.