Evaluation of Oryza sativa x O. glaberrima derived progenies for resistance to rootknot nematode and identification of introgressed alien chromosome segments using SSR markers

The genus Oryza has two cultivated species, Asian rice (Oryza sativa L.) and African rice (Oryza glaberrima Steud.) and 22 wild species. O. glaberrima is low yielding but has useful genes for resistance to biotic and abiotic stresses. Introgression lines derived from backcrossing of O. sativa x O. glaberrima, using O. sativa as recurrent parent, were evaluated for tolerance to root-knot nematode (Meloidogyne graminicola). Testing in sick plots infested with nematodes showed reduction in plant height, shoot and root biomass and leaf area index compared to the control. Based on gall rating and the ratio of the final population to the initial population of nematodes (Pf/Pi ratio), three introgression lines were found to be resistant to nematodes (IR80311-9-B-B-1-2 and IR80311-2-B-B-1-2 under screenhouse and IR80311-48-BB- 1 under phytotron conditions). Gall rating and the Pf/Pi ratio showed positive correlation (r = 0.61). Analysis of 122 introgression lines using simple sequence repeat (SSR) markers detected introgression of O. glaberrima segments into O. sativa

Effect of Sesbania rostrata on Hirschmanniella oryzae in Flooded Rice

Microplot experiments on flooded soil infested with Hirschmanniella oryzae were conducted to investigate the influence of the legum Sesbania rostrata as a rotation crop with rice, Oryza sativa L. cv. Moroberekan. To avoid a green manure effect from S. rostrata, all aerial parts were removed at harvest. The dry weight of paddy, culms and leaves, and number of culms of rice following Sesbania were 214%, 158%, and 121% greater, respectively, than those following rice. Ripening of the paddy occurred earlier if rice followed Sesbania. The beneficial effect of Sesbania may have been due to the trap-crop action of Sesbania against H. oryzae

Changes in biological factors of fertility in managed Eucalyptus plantations on a savanna soil in Congo

Biological factors of fertility were assessed through the study of litter quantity and quality, soil organic matter quantity and quality, soil microfauna, soil macrofauna, organic matter dynamic, particularly decomposition and non-symbiotic nitrogen fixation in an age series of Eucalyptus PF1 and one stand of E. urograndis (E. urophylla x E. grandis). The litter system underwent drastic changes with plot age: litter fall was higher in the older plots than in the younger ones. Soluble carbon and lignin content decreased significantly with plot age and decomposition rate increased. Change in soil organic matter amount occurred in the top layer of soil only and increased with plot age. This enhanced cation exchange capacity. Increase in soil organic matter content was due to the light organic fraction (>0.05 mm), and the amount of C did not change in the organo-mineral fraction. Soil organic matter quality changed also, and the C/N ratio increased with plot age. A drastic decrease in free living nematode density from savanna to young plantations was observed after which it increased slowly with plot age although in the 19-year-plots it was still about ten times lower than in savanna. The importance of Xiphinema parasetariae, a parasite of eucalypts, was confirmed. Its density increased markedly with plot age and the size of the patches where it occurred increased. All soil macrofauna, earthworms, termites and litter inhabiting groups, except the ant group, increased in density with plot age. Termite density decreased in logged stands but no other measured parameters showed any significant difference between plantations and clear felled areas. The long-term effect of harvesting was observed mainly in the litter system and it appeared to be strongly disturbed by previous logging. Previous logging did not affect soil organic matter and nematode populations, either free living or plant parasitic. Soil macrofauna groups slightly increased after harvesting. Total phenolic compounds and fibre content were very different in leaf litter among clones and hybrids