Allelopathic Effect of Conyza albida on Avena sativa and Spirodela polyrhiza

The allelopathic influence of four plant tissues of Conyza albida (stems, leaves and inflorescences) on oat growth were investigated using in vivo tests. Oat growth (fresh and dry weights of above and underground parts) was inhibited from phytotoxic activity of upper leaves and inflorescence tissues of C. albida in pot studies. The inhibition was significantly higher than in the other tissues studied. The inhibiting action of crude extracts and volatile compounds from young plants (rosette) and mature plants were examined using two bioassay methods: (a) seed germination and radicle growth of oat and (b) fresh weight of duckweed plants. Both bioassayed species exhibited greater phytotoxic response from the young plants, collected in winter, than from the mature ones.     

Vertical transmission of sublethal granulovirus infection in the tobacco caterpillar <Emphasis Type="Italic">Spodoptera litura</Emphasis>

Larvae that survived sublethal infection of Spodoptera litura granulovirus (SlGV) as 4th and 5th instars led to an increase in the larval period of treated larvae when compared with control. While pupal period and pupal weight remained unaffected, a significant alteration in sex ratio was observed. Although survivor moths could mate successfully, there was a significant reduction in the proportion of ovipositing females in treated larvae as compared with control. A significant reduction in fecundity of moths emerging from treated larvae was also noticed, but the egg viability was never influenced by the treatment. However, there was a significant increase in progeny mortality in treated larvae over control. The offspring mortality in survivors increased up to three subsequent generations but not thereafter. Hence, repeated field applications of inoculum are required. The implication of the present findings in terms of reduced fecundity coupled with increased larval development indicates that vertical transmission can lead to increased virus dispersal, both of which would reduce the host's innate capacity for population increase. This is particularly important in S. litura, which is a migratory species and occurs sporadically in a particular agro-ecosystem.