7. Utilization of va-mycorrhiza as a factor in integrated plant protection.
Agriculture, Ecosystems and Environment, 29, 1989, pp. 131-135
The natural growth area of rubber trees is the tropical rainforest of Brazil in which very poor soils are present. In preliminary studies it was shown that rubber trees form a VA-mycorrhiza under natural growth conditions. The influence of VAM on plant pathogen interactions has been studied for a number of plants but rarely on woody plant species and therefore no conclusive data for trees like Hevea brasiliensis are available. Young Hevea trees reveal a rhythmical growth pattern, in which leaf flushing occurs. Leaves are produced every 6 to 8 weeks and need about 4 weeks for maturation. Within this phase four developmental stages (A to D) can be distinguished by morphological characteristics.
The leaves are showing an expressed leaf age resistance to fungal attack. Stages A and B are generally susceptible to a high number of fungal pathogens, stage C is of intermediate resistance and stage D is not infectible by biotrophic leaf pathogens. In this study the influence of VAM inoculation, additionally to the indigenous VAM populations, plant growth, leaf development and resistance behaviour against Microcyclus ulei,the causal agent of the South American Leaf Blight, was evaluatd.
VA-mycorrhiza infected rubber trees reveal an increase in resistance against a foliar disease (South American Leaf Blight) caused by the ascomycete Microcyclus ulei. The lesion size and the production of spores of the pathogen were significantly lowered in VAM inoculated plants, whereas the number of lesions remained unchanged. This suggests that the resistance response of the plant is significantly influenced by VAM treatment and demonstrates that enhanced resistance is not due to inhibition of penetration or early growing phases of the pathogen but to the modification of late resistance responses.
The data presented here unequivocally show that the VAM-association causes physiological changes relevant to the resistance reactions in the leaves, even when no macroscopic modification of the plant can be seen.
The enhancement of the resistance of the plant along with the reduction of the pathogens spore production, here caused by a VAM-fungus, is an important epidemiological factor for the control of the South American Leaf Blight in rubber plantations of Brazil. The combination of VAM-inoculum with well designed plant management measures, crown budding, mixed cropping and the use of hyperparasites can lead to a complex system of integrated plant protection in Brazilian rubber cultivation.
1201 92 - 10/128
Asia, India, study, glasshouse, rice, leaf extracts, fungal pathogens
TEWARI, S.N. and M. NAYAK
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