Rhizosphere fungus Penicillium chrysogenum promotes growth and induces defence-related genes and downy mildew disease resistance in pearl millet.

Susceptible pearl millet seeds (cv 7042S) were treated with the plant growth promoting fungus Penicillium chrysogenum (PenC-JSB9) at 1 × 10(8) spores·ml(-1) to examine mRNA expression profiles of five defence responsive genes and test its ability to induce resistance to downy mildew caused by Sclerospora graminicola. PenC-JSB9 treatment at 1 × 10(8) CFU·ml(-1) for 6 h significantly enhanced seed germination (9.8- 89%), root length (4.08% to 5.1 cm), shoot length (18.9% to 7.77 cm) and reduced disease incidence (28%) in comparison with untreated controls. In planta colonisation of PenC-JSB9 showed that all three root segments (0-6 cm) and soil dilutions incubated on PDA produced extensive mycelial growth, however colonisation frequency of PenC-JSB9 was significantly higher in soil than in root segments. Spatiotemporal studies revealed that induction of resistance was triggered as early as 24 h and a minimum 2-3 days was optimal for total resistance to build up between inducer treatment and challenge inoculation in both experiments. In Northern blot analysis, transcript accumulation of resistant and PenC-JSB9 induced susceptible cultivars showed higher basal levels of defence gene expression than non-pretreated susceptible controls. Transcript accumulation in resistant seedlings challenge-inoculated with the pathogen showed maximum expression of CHS (3.5-fold increase) and Pr-1a (threefold increase) at 24 and 12 h, respectively. While PenC-JSB9 pretreated susceptible seedlings challenge-inoculated showed rapid and enhanced expression of LOX and POX at 48 h and for CHT at 24 h, whereas non-pretreated susceptible seedlings after pathogen inoculation showed weak expression of hybridised defence genes. Enhanced activation of defence genes by PenC-JSB9 suggests its role in elevated resistance against S. graminicola.

Anti-oomycete compounds from Ganoderma appalantum, a wood rot basidiomycete.

Solvent extracts of 17 different basidiomycetes were tested for their ability to inhibit Sclerospora graminicola. Among those tested, only three basidiomycete crude extracts exhibited significant inhibition on pathogen sporulation, zoospore release and zoospore motility. In vitro, the chloroform extract of Ganoderma appalantum (3 mg mL(-1)) recorded a maximum sporangial inhibition of 52.5 and 82.0% zoospore release and 92.5% motility. Crude extracts of three different basidiomycete fungi were treated to pearl millet seeds and assessed for seed germination, seedling vigour and effectiveness against downy mildew disease under greenhouse conditions. None of the solvent extracts were found to be phytotoxic. Chloroform and petroleum ether extracts of G. appalantum (3 mg mL(-1)) proved to be the best by offering disease protection of 55.6 and 43.7%, respectively, followed by chloroform and petroleum ether extracts of Polyphorus spp., with 42.5 and 39.1% disease protection. The thin layer chromatography (TLC) spots that developed were eluted and tested for inhibition of S. graminicola zoosporangia. The partially purified compound from TLC chloroform extract of G. appalantum consistently showed good inhibitory effect against S. graminicola, which exhibited inhibition of sporangia (42.3%), zoospore release (76.7%) and zoospore motility (86.7%), compared to the chloroform control which offered only 1.9, 2.9 and 1.7% inhibition of sporangia, zoospore release and zoospore motility, respectively. The partially purified compound from petroleum ether extract of G. appalantum resulted in 38.0, 63.0 and 81.6% inhibition of sporangia, zoospore release and motility, respectively, compared to petroleum ether control. However, azoxystrobin 250 SC (2 microg mL(-1)) and apron 35 SD (0.015 mg mL(-1)) treated on sporangial suspension showed the highest inhibition of S. graminicola pathogen compared to chloroform and petroleum ether TLC fractions.