First recorded in Egypt in the 1980s, Macrophomina crown and root rot of strawberry has increasingly challenged Californian farmers within the past decade, and even more recently in other strawberry-producing regions of the world. Strawberry growers in Chile, Argentina, and Spain have not escaped this outbreak either, but Dr. Marlene Rosales of the Pontifical Catholic University of Chile is working to find genetic resistance to the disease.
In the past, growers have controlled the strawberry’s many besetting diseases by frequent replanting and crop rotation in combination with soil fumigation with a methyl bromide and chloropicrin preparation like VAPAM®. Though effective, VAPAM® and its ingredients are also very hazardous and highly regulated. Many Californian growers who moved away from this fumigant in the early 2000s, however, soon ran into Macrophomina rot.
In a report published in July of last year (2016), a team of researchers from the University of California and the USDA-ARS dissected this very problem. They evaluated several isolates of Macrophomina phaseolina, the fungus that causes Macrophomina rot, and measured the rot-susceptibility of different strawberry varieties and several cover crops that are used in rotation with strawberry in California.
They found that strawberry-specific strains of M. phaseolina don’t infect fava bean, mustard, oat, rye, or vetch cover crops. This means that these cover crops are not causing the disease to proliferate in the absence of strawberries. Cover cropping and crop rotation, which are indispensable disease, weed, and pest-defeating agricultural practices, can therefore be effectively maintained as a part of the multi-pronged solution to defeat Macrophomina rot.
This team also found that at least one strawberry variety—‘Seascape’—is more resistant to M. phaseolina than several of its peers. Though in this case only distinguishable in earlier stages of growth (by the end of the eight-week experiment, all the tested varieties were equally diseased due to the severe inoculation method used), disease resistance that differs by variety indicates a genetic basis for resistance. And that’s where Chile comes in.
Doctor Marlene Rosales at the Pontifical Catholic University of Chile plans to parse out the genetics of M. phaseolina resistance in strawberry. Though her research may take any of a number of routes to fulfill this objective, the ultimate goal is to produce resistant varieties that will be used in conjunction with other control methods to economically and safely produce strawberries under the threat of Macrophomina rot.
Growers welcome any solution that stops the rot while lessening fumigation needs. As with other diseases and other crops, genetic resistance is the most economic, easiest to use, and most environmentally friendly solution.
I wish Dr. Rosales and her team the best of success in their quest.
I consulted the following sources for this post:
Koike, S.T., Arias, R.S., Hogan, C.S., Martin, F.N., and T.R. Gordon. 2016. Status of Macrophomina phaseolina on strawberry in California and preliminary characterization of the pathogen. International Journal of Fruit Science. 16(Supplement 1):148-159.