Ultrastructural studies on penetration sites of Neovossia indica, the partial bunt agent of wheat.
To elucidate the mode of penetration of N. indica into the host, five wheat cultivar/lines including a susceptible cultivar (WL711), a morphologically resistant line (R1: Altar 84 CD22344-A-8M-1Y-1M-1Y-2Y-1M-0Y) and three physiologically resistant lines (R2: 6811/RGB-U//WARD/3/FGO/4/RABI/5/CIGM89. 564-0Y; R3: CMH84.1106CMH84.1106-1Y-6B-1Y-2B-2Y-2B-0Y and R4: WEE/KOEL//WEAVERCMBW90M132-138M-010M) were inoculated by three different methods. The sequence of events that took place from post inoculation up to penetration was surveyed by scanning electron microscopy. Germination of allantoid secondary sporidia occurred normally on various spike parts in all three inoculation methods. Directional growth toward the stomata or the bulliform cells of glumes, lemma and rachis was not seen. Direct penetration through the epidermal cells of rachis, lemma and glumes, but not through ovarian walls was sporadically seen only in the susceptible cultivar. Hyphal anastomoses on the glumes and rachis surface of all cultivars were occasionally observed. Penetration of sporidial germ tubes and hyphae through stomata was observed. Entrance of germ tube and hyphae to the bulliform cells was also seen. In most cases, hyphae that tended to penetrate the stomata, actually extruded out instead and frequently true penetration was not observed. This indicates that infection development may take place only when two compatible hyphae are anastomosed in the early stages of penetration. In physiologically resistant lines examined in this study, disease did not develop, even after penetration of the spike by the fungus. This indicates that resistance mechanism to N. indica in wheat might become operative only after penetration.
Ali Moosawi-Jorf
S
S
Department of Plant Protection, Shahid Chamran University, Ahwaz, Iran.
Alizadeh
A
A
Farrokhi-Nejad
R
R
Pour-Jam
E
E
D005658:Fungi / Q000472:pathogenicity* / Q000502:physiology; D018525:Germination; D008855:Microscopy, Electron, Scanning; D014908:Triticum / Q000382:microbiology* / Q000648:ultrastructure*