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Pathogenesis and Host-Parasite Relations of the Cyst Nematode, Heterodera graminophila, on Grasses. W. Birchfield, ARS, USDA, and the Department of Plant Pathology, Louisiana State University, Baton Rouge, Louisiana 70803; Phytopathology 63:38-40. Accepted for publication 13 July 1972. DOI: 10.1094/Phyto-63-38.

A recently described cyst nematode, Heterodera graminophila, parasitized barnyard grass, Echinochloa colonum. Larvae penetrated roots and became oriented along the vascular cylinder in 12 days with sausage-shaped females developing within 18 days. The white, lemon-shaped cysts emerged through the epidermis leaving a crevice in the root at the infection site after the cyst was dislodged. A few eggs were left on the epidermis or in the crevice after 24 days, but most remained inside the cysts. Neither galling of host tissues, secretion of a gelatinous matrix around the eggs, nor giant cells around the feeding site were associated with H. graminophila. Necrosis of host-tissues was noticed in the pericycle and cortex, and a slight enlargement of the phloem occurred near the head of the nematode; no foliage symptoms were observed. Roots were generally parasitized by large numbers of nematodes at all stages of development. Secondary infection developed after 64 days; a few brown cysts were found at that time. Cell walls of the pericycle were thickened as evidenced by heavier stain. Males did not penetrate to the vascular area, but remained in the cortex near the epidermis where they molted and developed to maturity. Developing males fed only in the cortical parenchyma. Other host grasses were rice, Oryzae sativa, and Johnson grass, Sorghum halapense.