Interaction between Pyricularia oryzae, four Helminthosporium species and Curvularia lunata in rice leaves

Abstract

The interaction between six fungal parasites of rice: Pyricularia oryzae, Helminthosporium oryzae, H.
sativum, H. spiciferum, H. australiensis and Curvularia lunata was studied quantitatively by a modified plant ecology
technique known as the de Wit replacement series. Each fungus was inoculated alone or in combination with one
of the other five fungi in various proportions into rice plants under experimental conditions. Leaves developing
lesions were harvested and incubated in a moist chamber. The yield of each fungus was its conidial production on the
rice leaves. The artificial inoculations indicated that interactions between the pathogens in the mixture could be
beneficial, antagonistic, or null. Interspecific interaction (i.e. antagonism) occurred in the majority of paired combinations
(H. oryzae + P. oryzae; H. sativum + H. spiciferum, H. australiensis, C. lunata or P. oryzae; H. australiensis +
H. spiciferum, C. lunata or P. oryzae; and P. oryzae + C. lunata). The relative yield total (RYT) lines were significantly
lower than the expected value, which is 1. The RYT lines were concave upward, revealing a beneficial effect of one or
both pathogens on the other, when H. oryzae was in mixture with H. sativum or H. spiciferum. A null effect between
fungi occurred in four combinations (H. oryzae + H. australiensis or C. lunata; H. spiciferum + C. lunata; and P.
oryzae + H. spiciferum) showing that with these combinations inter- and intraspecific competitions were equal in
intensity. Thus, the de Wit replacement series technique indicated that it was possible to quantify the interaction
between all the pathogenic fungi tested.