Suppression of Phytophthora root rot in avocado (Persea indica) and microbial profiling the soil following addition of soil additives

Qurrat Ul Ain Farooq1,2, Jen McComb1 and Giles E. St.J. Hardy1, Treena I Burgess1

1Phytophthora Science and Management, Environmental and Conservation Sciences, Murdoch University, Perth, WA, 6150, Australia.
2Institute of Agricultural Sciences, University of the Punjab, Lahore, Pakistan.

Abstract:
Integrated management approaches for the control of Phytophthora root rot, one of the worst avocado diseases worldwide, will increase sustainability and reduce economic losses. We tested the ability of microbial or mineral-based soil additives to suppress root rot caused by P. cinnamomi and did microbial profiling of the soil of selected treatments in a subsequent experiment. Phosphite and metalaxyl treatments for the control of disease, and glyphosate for weed control were also assessed. Soil treatments were applied to 9-month old avocado saplings growing in containers in a glasshouse. After one-month, half of the plants of each treatment were inoculated with the pathogen. Three months after inoculation, plants were harvested and fine root and total root dry weight and root damage were assessed. Inoculation with P. cinnamomi resulted in a reduction of shoot and root growth in all treatments except in soils top- dressed with either of two mineral conditioners both of which contained silicon. Other soil additives gave no additional protection from Phytophthora damage over that provided by application of mulch from an avocado orchard. This mulch was derived from decomposed wood mulch, chicken manure and avocado leaf litter. Phosphite was preferable to metalaxyl as a chemical treatment, as the latter reduced shoot and root growth of non-infected plants. Glyphosate reduced shoot and fine root growth of both non-infected and infected plants. The effectiveness of the avocado mulch, and of the silcon-based mineral mulches for disease suppression was checked in a repeated experiment and the microbial communities in these rhizospheres and soils analysed using metabarcoding analysis. This demonstrated the bacterial communities were very different among different treatments and significantly more diverse in treatments where Phytophthora has been supressed.


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