Development of a marker assisted selection program for cacao

ABSTRACT Production of cacao in tropical America has been severely affected by fungal pathogens causing diseases known as witches' broom (WB, caused by Moniliophthora perniciosa), frosty pod (FP, caused by M. roreri) and black pod (BP, caused by Phytophthora spp.). BP is pan-tropical and causes losses in all producing areas. WB is found in South America and parts of the Caribbean, while FP is found in Central America and parts of South America. Together, these diseases were responsible for over 700 million US dollars in losses in 2001 (4). Commercial cacao production in West Africa and South Asia are not yet affected by WB and FP, but cacao grown in these regions is susceptible to both. With the goal of providing new disease resistant cultivars the USDA-ARS and Mars, Inc. have developed a marker assisted selection (MAS) program. Quantitative trait loci have been identified for resistance to WB, FP, and BP. The potential usefulness of these markers in identifying resistant individuals has been confirmed in an experimental F(1) family in Ecuador.     

Influence of variety on the within-plant distribution of cassava green spider mite (Acari: Tetranychidae), and leaf anatomical characteristics and chemical components in relation to varietal resistance

The within-plant distribution of the cassava green spider mite, Mononychellus tanajoa Bondar, and the anatomical characteristics and the chemical components relating to varietal resistance of cassava, were studied using 11 cassava genotypes with varying levels of resistance for two dry seasons and one wet season. The results show that M. tanajoa aggregates on the top leaves of cassava at low levels of resistance as compared with a more even within-plant distribution at higher levels of resistance. Thus, for accurate sampling of mite populations, it might be important to consider young and old leaves, not just the young leaves, in fields containing resistant and susceptible cassava genotypes. Correlations between the anatomical characteristics and mite population density and damage scores were not consistent across months, either within or over seasons. This suggests that leaf anatomical characteristics may not be important in the varietal resistance of cassava to M. tanajoa. During the dry season, mite population density was positively correlated with leaf nitrogen, potassium and phosphorus and negatively correlated with leaf calcium and fat. Only calcium was negatively associated with mite damage at the peak of the dry season (January 1993 and 1994). Breeding cassava genotypes with high levels of leaf calcium and fat, and low levels of leaf nitrogen, potassium and phosphorus, may improve the level of resistance to M. tanajoa.     

Assessment of salt tolerance of <Emphasis Type="Italic">Aegilops</Emphasis> L. from the VIR collection

The effect of high NaCl concentrations on accumulation of biomass and change in content of sodium and potassium ions in 17 accessions of nine species of Aegilops L. is studied. Three salt-tolerant accessions (Ae. tauschii k-677 and 674 and Ae. cylindrica k-676) containing the D genome and having a high K/Na ratio are identified.     

Uleine and demethoxyaspidospermine from the bark of Plumeria lancifolia

The isolation of (+)-uleine (1) and (+)-demethoxyaspidospermine (2) from the bark of Plumeria lancifolia is reported along with (1)H- and (13)C-NMR data.     

Effect of harvest date on onion yield in a northern climate

Summary

Timing of harvest is an essential factor affecting the quantity, quality and storability of onion yield. This study aimed to establish when no further yield increase is to be expected and to determine the relationship between maturity stage and yield development. Experiments on 4-6 harvests at 9-14 d intervals were conducted at several locations in southern Finland in 1996-1999. Generally little, if any, yield increase was recorded after plants had reached 100% maturity, but in some cases bulb growth continued after complete fall-down of leaves. On the other hand, harvesting before 100% maturity resulted in a yield loss of 0-45% of final yield. Weight loss, and thus energy consumption during drying, was still reduced after complete leaf fall-down. Therefore, it may be concluded that delaying harvest up to 100% maturity, or even longer, ensures that highest yield and lowest drying costs.