Phenotypic variability of Leptosphaeria lindquistii (anamorph: Phoma macdonaldii), a fungal pathogen of sunflower

Abstract

Growth of 17 isolates of Phoma macdonaldii, the causal agent of sunflower black stem, was investigated for response to pH and temperature, and for morphology and asexual morphogenesis (pycnidiogenesis and pycnidium size). For all isolates, the optimum pH for growth was between 4 and 5, and the optimum temperature varied between 20 and 30ЊC and radial growth was slowest at 5 and 35ЊC. Significant differences in the number and size of pycnidia were observed between isolates. Pycniospore germination was investigated under various conditions in five isolates chosen for their geographical origins, pigmentation, optimum growth temperature and pycnidiogenesis. Increasing the concentration from 10 6 to 10 7 pycniospores per mL decreased the germination rate. The optimum temperature for pycniospore germination varied between 15 and 30ЊC, depending on the isolate, and the optimum and maximum pH values were 5 and 7, respectively. The optimum and minimum relative humidities allowing pycniospore germination were 100 and 95%, respectively. Pycniospore germination was photo-independent. An artificial inoculation method was developed and the aggressiveness of the pathogen was assessed on a susceptible sunflower cultivar, using a 1-9 scale that integrated the percentage of necrotic area on the cotyledon petiole at the stage when the first pair of leaves was fully developed. Significant differences in aggressiveness were observed among the 17 isolates. The parameters investigated clearly suggest the occurrence of a wide phenotypic variability in Phoma macdonaldii.

Testing sunflower inbred lines for tolerance to Phoma black stem

“…In addition, they showed that the behaviour of sunflower genotypes in controlled conditions remained unchanged irrespective of the phenological stage reached at the time of inoculation. Most of field testing is usually done at the stage R3-R5 (Carson, 1991;Sessau et al, 2008), as we did as well, but a vast majority of studies have been done in controlled conditions (Mirić et al, 1999;Roustaee et al, 2000a). Furthermore, our results from the non-irrigated field, compared to the irrigated one, are in concordance with the results of Sessau et al (2010), who found a positive correlation between water stress and P. macdonaldii attack severity.…”

“…Besides differences in sunflower genotype response, certain variability has also been proved to exist among different isolates of the fungus (Roustaee et al, 2000a;Larfeil et al, 2002). Therefore, accurate knowledge of the pathogen variability is also required for identification of tolerant genotypes.…”

Genotype‐isolate interaction for resistance to black stem in sunflower (Helianthus annuus)

“…The constancy of ranking of isolates over the two experiments in this study provides further strong evidence for this claim. Similar variation in aggressiveness was demonstrated among isolates of P. macdonaldii originating from different geographical locations based on pathogenicity tests on cotyledon petioles (Roustaee et al, 2000b;Larfeil et al, 2002).…”

Factor Affecting Growth of Phoma cajani Causing Stem canker in Pigeonpea

“…According to Roustaee et al, (2001) for 17 isolates of Phoma macdonaldii, the causal agent of sunflower black stem, the optimum pH for growth was between 4 and 5 but in the present study none of the isolates were found to grow at best at that pH.…”

“…In the past Nebane and Ekpo (1995) investigated the effects of temperature on radial growth and pycnidium production of cowpea (Vigna unguiculata) isolates (PB1, PB2, PB3) of Phoma bakeriana in vitro and found that maximum growth and pycnidium production occurred at 25 0 C. The optimum temperature range was 20C to 28 0 C for the growth of Phoma as deduced by KueiMai (2000). Roustaee et al, (2001) evaluated the growth of 17 isolates of Phoma macdonaldii, the causal agent of sunflower black stem and investigated for response to temperature and for morphology and asexual morphogenesis (pycnidiogenesis and pycnidium size). They concluded that the optimum temperature varied between 20 and 30°C and radial growth was slowest at 5 and 35°C.…”