Hyaluronidase and protease activities from Indian snake venoms: neutralization by Mimosa pudica root extract

The aqueous root extract of Mimosa pudica dose dependently inhibited the hyaluronidase and protease activities of Indian snakes (Naja naja, Vipera russelii and Echis carinatus) venom.     

Marker‐assisted introgression of bacterial blight and blast resistance into IR 58025B,an elite maintainer line of rice

IR 58025A is a very popular wild‐abortive cytoplasmic male sterile (WA‐CMS) line of rice and is extensively used for hybrid rice breeding. However, IR 58025A and many hybrids derived from it possess mild aroma (undesirable in some parts of India) and are highly susceptible to bacterial blight (BB) and blast diseases. To improve IR 58025A for BB and blast resistance, we have introgressed a major dominant gene conferring resistance against BB (i.e. Xa21) and blast (i.e. Pi54) into IR 58025B, the maintainer line of IR 58025A. An introgression line of Samba Mahsuri (i.e. SM2154) possessing Xa21 and Pi54 genes in homozygous condition and fine‐grain type was used as donor parent, and backcross breeding strategy was adopted for targeted introgression of the resistance genes. PCR‐based molecular markers tightly linked to Xa21 and Pi54 were used for selection of BB‐ and blast‐resistant lines, while closely linked markers were used for identification of backcross‐derived plants devoid of Rf4 and aroma. At BC₂F₅, four backcross‐derived lines possessing resistance against BB and blast, devoid of aroma, high yield, short plant stature, long‐slender grain type and with recurrent parent genome recovery ranging from 88.8% to 98.6% were selected and advanced for further evaluation. The improved versions of IR 58025B, viz. SB54‐11‐143‐9‐44‐5, SB54‐11‐143‐9‐44‐98, SB54‐11‐143‐9‐44‐111 and SB54‐11‐143‐9‐44‐171, behaved as perfect maintainers when test‐crossed with WA‐CMS lines. Agronomically superior lines of improved IR 58025B are being converted to CMS line through backcrossing for developing high‐yielding and biotic stress‐resistant rice hybrids.     

Differential effects of soil properties on leaf nitrogen release

 Identifying the determinants of the N dynamics of plant prunings or litter is important for the efficient management of agroecosystems in order to improve their productivity. The plant materials in these ecosystems are managed as soil surface mulches or are incorporated into the soil. Numerous studies have been conducted to investigate which plant chemical parameter best governs N release. In these studies, different plant materials have been incorporated into a soil with a set of known characteristics. The objective of the present study was to examine the effects of different soil properties on N release from plant leaves, when they were incorporated into soils under non-leaching conditions. A laboratory incubation experiment (for 8 weeks) was carried out with dried and ground leaves of six leguminous plants and wild sunflower, which were mixed with three soils (alfisol; ultisol, udult; ultisol, humult). Leaf cellulose was the major chemical parameter that determined leaf N release in the alfisol and ultisol, udult. In the ultisol, humult, the C/N ratio and hemicellulose concentration were better related to N release. Cellulose was not a good indicator of N release in the ultisol, humult, possibly due to a low soil pH which did not favour the activity of the cellulose-degrading enzymes of microbes active in decomposition. Soil pH determined the specific C source that was used to generate energy for microbial action and N mineralization/immobilization. It also had an effect on the nitrification of the mineralized N. The levels of labile soil C fractions governed the mode or nature of N release (i.e. mineralization or immobilization). The levels of labile leaf C fractions incorporated into the soils governed the extent of N release. The soil N concentration in the decomposable organic matter pool, as compared to the leaf N concentration, determined whether leaf N limited its own release. It is recommended from this study that, in grouping different leaf materials as sources of N, the properties of soils into which they are incorporated should also be considered, in addition to leaf quality in terms of its chemical composition. In future studies, the relationships identified under laboratory conditions in this experiment should be verified under field conditions. Received: 3 December 1997