Genetic divergence of rubber tree estimated by multivariate techniques and microsatellite markers

Genetic diversity of 60 Hevea genotypes, consisting of Asiatic, Amazonian, African and IAC clones, and pertaining to the genetic breeding program of the Agronomic Institute (IAC), Brazil, was estimated. Analyses were based on phenotypic multivariate parameters and microsatellites. Five agronomic descriptors were employed in multivariate procedures, such as Standard Euclidian Distance, Tocher clustering and principal component analysis. Genetic variability among the genotypes was estimated with 68 selected polymorphic SSRs, by way of Modified Rogers Genetic Distance and UPGMA clustering. Structure software in a Bayesian approach was used in discriminating among groups. Genetic diversity was estimated through Nei's statistics. The genotypes were clustered into 12 groups according to the Tocher method, while the molecular analysis identified six groups. In the phenotypic and microsatellite analyses, the Amazonian and IAC genotypes were distributed in several groups, whereas the Asiatic were in only a few. Observed heterozygosity ranged from 0.05 to 0.96. Both high total diversity (HT' = 0.58) and high gene differentiation (G st' = 0.61) were observed, and indicated high genetic variation among the 60 genotypes, which may be useful for breeding programs. The analyzed agronomic parameters and SSRs markers were effective in assessing genetic diversity among Hevea genotypes, besides proving to be useful for characterizing genetic variability

The Speargrass (Imperata cylindrica (L) Beauv.) menace in Ghana: Incidence, farmer perceptions and control practices in the forest and forest-Savanna transition Agro-ecological Zones of Ghana

Surveys to determine farmers’ practices, perceptions and the incidence of speargrass were conducted in the forest and forest-savanna transition zones of Ghana in 1996 and 2000. Mean farm size was 1.2 ha, fallow and cropping length was 4.7 and 4.5 years, respectively, with a mean cropping intensity factor (CIF) of 49%. Speargrass had been present in the area for over 40 years and was perceived as the most noxious weed. Eighty- six percent of fields that relied on slash-burn method of land preparation had severe speargrass infestation. Infestations > 50% cover, mean density of 33 plants m-2 and shoot height range of 15–300 cm were observed on 60% of the fields. Fifty-one percent of farmers reported of inadequate level of control with current control practices. Glyphosate was applied onfields with > 50% speargrass cover. Speargrass becomes a problem after 3 years continuous cropping from fallow and, under severe infestation, most farmers abandon fields to natural fallow. A dense regrowth of Chromolaenaodorata is indicative of a speargrass-suppressed field. Follow-up weed control could be 3-6 times/season depending on initial land preparation, type of crop and/or level of infestation. Cost of weed control was 20–60% higher on speargrass-infested field ($71/weeding/ha) than on other fields, and weeding may take 20–25 mandays/ha. Farmers perceived average yield losses of 30–80$31–$84,$155–$414 and$272–$727 for maize, cassava and yam systems, respectively. Reductions in food quality due to the piercing nature of the rhizomes was also paramount

Clonal stability of latex yield in eleven clones of Hevea brasiliensis Muell. Arg.

Eleven Hevea brasiliensis clones were evaluated for clonal stability of latex yield. A randomized complete block design was used with four replicates, two locations, seven years and three periods per year. Stability analysis was based on clone x year and clone x year x location interactions. Five stability parameters viz environmental variance, shukla's stability variance, regression of clonal latex yield on environmental index, variance due to regression and variance due to deviation from regression were applied. There was significant clone x environment effect at the two levels of interaction. Among the eleven clones, C 162 was outstanding for clonal stability and it can serve as donor parent for stability alleles. Three clones (C 76, C 150 and C 154) were also stable. The four stable clones (C 76, C 150, C 154 and C 162) are suitable for broad-spectrum recommendation for latex yield. Five clones (C 83, C 143, C 163, C 202 and RRIM 600) will require environment-specific recommendation because of their unstable phenotype. The stability feature of two clones (C 145 and C 159) was not clear and this will be investigated in subsequent studies