Biosolarization as an alternative method to inhibit parasitic Phelipanche ramosa germination

Abstract

Phelipanche ramosa, or branched broomrape, is a parasitic weed that attaches to the roots of host plants and can cause great agricultural losses, from reduced yield to crop termination without harvest. Conventional approaches to manage broomrape infestations include fumigation with toxic compounds, such as methyl bromide. Solarization has been used as well, but can leave a field out of service for entire seasons. Biosolarization is an alternative pest management strategy with a shorter timeframe that can reduce the need for fumigants and preplant herbicides by amending soil with organic matter, covering with a clear tarp, and irrigating. Weed seeds subjected to biosolarization experience a variety of stresses –including biocidal organic acids, high temperatures, and low oxygen– that can prevent future germination. This study evaluated the application of biosolarization with two different amendments, three amendment rates, and three temperatures for reduction of P. ramosa germinability. Simulated biosolarization was carried out in anaerobic bioreactors of wetted and amended soil with seeds incorporated. Tomato pomace and spent mushroom substrate were used as the organic matter amendments. Soil pH, electrical conductivity, and production of biocidal organic acids were evaluated before and after biosolarization, alongside germination capacity of P. ramosa seeds. Soil metrics of biosolarization treatments were compared to unamended, solarized soil and seed germination capacity was compared to that of untreated, control seeds. Broomrape germination is triggered by strigolactone, a plant hormone released into the rhizosphere. Therefore, a strigolactone analog was used to test the germinability of the treated seeds in absence of a host. To isolate the effects of biocidal organic acid exposure on broomrape germinability, seeds were also exposed to the acids produced during biosolarization, but without the added thermal and low oxygen stresses. The results suggest that biosolarization is an effective method to reduce P. ramosa germinability by >99% with amendment rates as low as 1.0% by dry weight and temperatures of 35°C, which can inform future validation in field studies. Use of biosolarization may help protect the production of host plants on an infested field, while reducing the need for toxic compounds or lengthy treatments.