A cytological study of compatible and incompatible interactions between Sorghum bicolor and Colletotrichum sublineolum

Abstract

SUMMARYCytological and physiological studies were conducted on the infection process of Colletotrichum sublineolum P. Henn. Kabat et Bub. on susceptible and resistant cultivars of Sorghum hicolor (L.) Moench. Compatible interactions were characterized by an early biotrophic phase lasting c. 24 h, during which intracellular infection vesicles and prin-iary hyphae colonized epidermal cells. 7 hinner secondary hyphae were first observed branching out from primary hyphae after 66 h. These hyphae proliferated throughout the epidermis and into underlying mesophyll cells. Secondary hyphae were associated with host cell death and the onset of a necrotrophic phase. Pigmented cytoplasmic inclusions, thought to represent the host defence response, were also first observed at 66 h, although there was little apparent effect on subsequent fungal colonization of tissue. By 90 h, secondary hyphae had proliferated throughout the leaf sheath, with production of necrotic lesions and acervuli. In incompatible interactions, infection vesicles formed inside epidermal cells within 42 h of inoculation but there was no evidence for a biotrophic interaction as penetrated cells appeared dead and fungal developmer>t was restricted to single epidermal cells. Host defence responses were observed earlier than in compatible interactions: heavily pigmented (dark red) cytoplasmic inclusions were distributed throughout penetrated cells at 42 h. By 66 h, these cytoplasmic inclusions had disintegrated and dark red pigment had spread throughout the cell. Concurrent with the disintegration of the cytoplasmic inclusions was the disruption of the cytoplasm of both the host cell and the fungus. Further fungal development was restricted. These observations are discussed in relation to the importance of the initial biotrophic phase in the successful colonization of S. bicolor by C. sublineolum and the role of the host defence response in preventing colonization.

Temporal synthesis and radiolabelling of the sorghum 3‐deoxyanthocyanidin phytoalexins and the anthocyanin, cyanidin 3‐dimalonyl glucoside

“…The rapid increase in accumulation of the two luteolinidin compounds between 24 and 48 hpi is significant, as it corresponds to the time of attempted penetration and intracellular growth of the fungal pathogen (Wharton & Julian, 1996). These authors showed that in the resistant cv.…”

Infection induced oxidative cross-linking of hydroxyproline-rich glycoproteins (HRGPs) is associated with restriction ofColletotrichum sublineolumin sorghum

“…The pathogen is classified as a hemibiotroph, with an initial, symptomless biotrophic phase, with thick intracellular primary hyphae. This is followed by development of inter-and intracellular thin necrotrophic secondary hyphae (Wharton and Julian 1996;Wharton et al 2001). Recently, we studied the infection biology and initial defense responses including induction of peroxidase activity and ROS accumulation in response to C. sublineolum infection in three genotypes of sorghum varying in resistance to the pathogen (P. Basavaraju, N.P.…”

Flavonoid Phytoalexin-Dependent Resistance to Anthracnose Leaf Blight Requires a Functional yellow seed1 in Sorghum bicolor

“…The contribution of flavonoid phytoalexins to resistance against Colletotrichum sublineolum in sorghum has been investigated by comparing the response of several sorghum cultivars that differentially produce 3-deoxyanthocyanidins (Wharton and Julian 1996;Tenkouano et al 1998;Lo et al 1999;Basavaraju et al 2009). These studies, although performed on nonisogenic lines, indicated that phytoalexin production in the resistant cultivars was not only more rapid but also more intense than in the susceptible lines.…”