Brown leaf spot disease and fertilizer interaction in irrigated rice growing on different soil types
Studies have been undertaken in a 1000 ha area of irrigated rice (Oryzica sativa) at Caroni (1975) Limited to determine the effect of the fertilizer programme on the incidence of important diseases. Over a period of three years higher levels of brown leaf spot (Cochliobolus miyabeanus) on rice varieties Oryzica 1 and Oryzica 5 on three different soil types were associated with increasing levels of leaf P, from a low of 0.149% of dry matter (DM) to a high of 0.396% DM. On the Washington silty clay loam series (Inceptisol) brown leaf spot incidence was lowest when leaf P was between 0.135% and 0.149% of DM. However, disease incidence was higher when leaf P levels fell to 0.133% of DM or rose above 0.149%, under conditions where N was more than adequate. The moderate levels of the disease experienced over the period had no effect on yield, as grain infection was minimal. The results support the conclusion that the incidence of brown leaf spot on irrigated rice at Caroni is influenced by sub-optimal levels paticularly of P. Careful monitoring and managememt of P nutrition is seen as an important part in the overall strategy for controlling the disease.
Molecular analysis of QTLs associated with resistance to brown spot in rice (Oryza sativa L.)
Helminthosporiosis or brown spot disease is widely distributed and is known to cause heavy yield losses in rice. In present investigation, a set of 154 doubled haploid (DH) lines derived from a cross between CT 9993-5-10-1M and IR 62266-42-6-2 was used to identify quantitative trait loci (QTLs) for brown spot disease. DH lines along with parents were planted in two different soil environments with two replications each in RCBD and evaluated for the brown spot resistance. We have identified total 10 QTLs for brown spot resistance using MAPMAKER/QTL 1.1 distributed over the eight chromosome of rice. Out of 10 QTLs, four were consistently discovered in both the soil types. The QTL BSq4.1 and BSq11.1 located on the chromosome 4 and 11 were identified in both the environment with higher LOD score and phenotypic variance and will be good candidates for fine mapping and positional cloning studies.
Rice disease situation in mangrove and associated swamps in Sierra Leone
Abstract The importance of mangrove swamp rice cultivation in Sierra Leone and in the West African subregion in general is defined and diseases occurring are listed and discussed including some indication of their economic importance. Generally it was observed that disease severity was less pronounced under this cultivation than in other types of rice growing areas. Several factors were considered responsible for this phenomenon, namely: the non‐use of nitrogenous fertilizers in mangrove swamp rice fields by the farmers; the breezy nature of the swamp environment which leads to faster drying up of water drops on the rice plant thus inhibiting the infection process; and the low pH and salinity, which, particularly in the off‐season, is thought to reduce the number of viable propagules of several rice pathogens. Rokupr was found to be suitable for the screening of rice varieties resistant to rice blast (Magnaporthe grisea (Hebert) M. E. Barr) due to the presence of a rich flora of races of the fungus. A str...