Diversity of Expression Types of Ht Genes Conferring Resistance in Maize to Exserohilum turcicum

Abstract

Northern corn leaf blight (NCLB) is an important leaf disease in maize (Zea mays) worldwide and is spreading into new areas with expanding maize cultivation, like Germany. Exserohilum turcicum, causal agent of NCLB, infects and colonizes leaf tissue and induces elongated necrotic lesions. Disease control is based on fungicide application and resistant cultivars displaying monogenic resistance. Symptom expression and resistance mechanisms differ in plants carrying different resistance genes. Therefore, histological studies and DNA quantification were performed to compare the pathogenesis of E. turcicum races in maize lines exhibiting compatible or incompatible interactions. Maize plants from the differential line B37 with and without resistance genes Ht1, Ht2, Ht3, and Htn1 were inoculated with either incompatible or compatible races (race 0, race 1 and race 23N) of E. turcicum. Leaf segments from healthy and inoculated plants were collected at five different stages of infection and disease development from penetration (0–1 days post inoculation - dpi), until full symptom expression (14–18 dpi). Symptoms of resistance responses conveyed by the different Ht genes considerably differed between Ht1 (necrotic lesions with chlorosis), Ht2 (chlorosis and small lesions), Ht3 (chlorotic spots) and Htn1 (no lesions or wilt-type lesions). In incompatible interactions, fungal DNA was only detected in very low amounts. At 10 dpi, DNA content was elevated in all compatible interactions. Histological studies with Chlorazol Black E staining indicated that E. turcicum formed appressoria and penetrated the leaf surface directly in both types of interaction. In contrast to incompatible interactions, however, the pathogen was able to penetrate into xylem vessels at 6 dpi in compatible interactions and strongly colonized the mesophyll at 12 dpi, which is considered the crucial process differentiating susceptible from resistant interactions. Following the distinct symptom expressions, resistance mechanisms conferred by Ht1, Ht2, Ht3, and Htn1 genes apparently are different. Lower disease levels and a delayed progress of infection in compatible interactions with resistant lines imply that maize R genes to E. turcicum are associated with or confer additional quantitative resistance.

The role of plant labile carbohydrates and nitrogen on wheat-aphid relations

“…7 ). Under the experimental conditions of Navarro et al 13 , R. padi fecundity measured in a setting similar to our assay 1 declined in wheat grown under [CO 2 ] = 800 ppm compared to controls at 400 ppm and high nitrogen supply partially offset the effect of elevated [CO 2 ].…”

“…The decupling of trophic webs is a conspicuous, ecologically and agronomically significant effect of global change 6 – 9 . Air CO 2 concentration [CO 2 ], ambient temperature, availability of water and nitrogen influence the plant phenotype with bottom-up consequences for the behaviour and fitness of herbivorous arthropods 9 – 13 .…”

“…Waring and Cobb 10 highlight the difficulty in predicting sign and magnitude of interactions, with significant interactions—whether positive, negative, or non-linear—in 338 out of 450 cases for herbivores feeding on water- or nutrient-stressed plants. Elevated [CO 2 ], high temperature and nitrogen deficit alter plant nutritional quality and secondary metabolites 9 , 11 – 13 . However, the impact of elevated [CO 2 ] interacting with temperature or nitrogen on insects, mediated by changes in plant phenotype, cannot be deduced from the effects of the individual factors 13 , 14 .…”

“…Elevated [CO 2 ], high temperature and nitrogen deficit alter plant nutritional quality and secondary metabolites 9 , 11 – 13 . However, the impact of elevated [CO 2 ] interacting with temperature or nitrogen on insects, mediated by changes in plant phenotype, cannot be deduced from the effects of the individual factors 13 , 14 . Furthermore, insect responses to host plants under elevated [CO 2 ] are guild-dependent 12 .…”

Histological characterization of the early‐stage infection events of Setosphaeria turcica in maize

“…Subsequently, the invasive hyphae enter the adjacent cells and xylem vessels (Hilu & Hooker, 1964;Knox-Davies, 1974;Kotze et al, 2019;Navarro et al, 2020). However, maize cell viability is not clear during S. turcica infection within 1 dpi, and some studies lacked statistical analysis of infection sites.…”