Pythiogeton ramosum, a new pathogen of soft rot disease of ginger (Zingiber officinale) at high temperatures in Australia

Pythium soft rot (PSR) of ginger caused by a number of Pythium species is of the most concern worldwide. In Australia, PSR outbreaks associated with Pythium myriotylum was recorded in 2007. Our recent pathogenicity tests in Petri dishes conducted on ginger rhizomes and pot trials on ginger plants showed that Pythiogeton (Py.) ramosum, an uncommon studied oomycete in Pythiaceae, was also pathogenic to ginger at high temperature (30–35 °C). Ginger sticks excised from the rhizomes were colonised by Py. ramosum which caused soft rot and browning lesions. Ginger plants inoculated with Py. ramosum showed initial symptoms of wilting and leave yellowing, which were indistinguishable from those of Pythium soft rot of ginger, at 10 days after inoculation. In addition, morphological and phylogenetic studies indicated that isolates of Py. ramosum were quite variable and our isolates obtained from soft rot ginger were divided into two groups based on these variations. This is also for the first time Py. ramosum is reported as a pathogen on ginger at high temperatures.

Developing effective fumigation protocols to manage strongly phosphine-resistant Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae)

BACKGROUND The emergence of high levels of resistance in Cryptolestes ferrugineus (Stephens) in recent years threatens the sustainability of phosphine, a key fumigant used worldwide to disinfest stored grain. We aimed at developing robust fumigation protocols that could be used in a range of practical situations to control this resistant pest. RESULTS Values of the lethal time to kill 99.9% (LT99.9, in days) of mixed-age populations, containing all life stages, of a susceptible and a strongly resistant C. ferrugineus population were established at three phosphine concentrations (1.0, 1.5 and 2.0 mg L−1) and three temperatures (25, 30 and 35 °C). Multiple linear regression analysis revealed that phosphine concentration and temperature both contributed significantly to the LT99.9 of a population (P < 0.003, R2 = 0.92), with concentration being the dominant variable, accounting for 75.9% of the variation. Across all concentrations, LT99.9 of the strongly resistant C. ferrugineus population was longest at the lowest temperature and shortest at the highest temperature. For example, 1.0 mg L−1 of phosphine is required for 20, 15 and 15 days, 1.5 mg L−1 for 12, 11 and 9 days and 2.0 mg L−1 for 10, 7 and 6 days at 25, 30 and 35 °C, respectively, to achieve 99.9% mortality of the strongly resistant C. ferrugineus population. We also observed that phosphine concentration is inversely proportional to fumigation period in regard to the population extinction of this pest. CONCLUSION The fumigation protocols developed in this study will be used in recommending changes to the currently registered rates of phosphine in Australia towards management of strongly resistant C. ferrugineus populations, and can be repeated in any country where this type of resistance appears. © 2014 Commonwealth of Australia. Pest Management Science © 2014 Society of Chemical Industry