Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 2/25/2014
Publication Date: 7/8/2014
Citation: Mazzola, M., Strauss, S.L. 2014. Replant disease control and system resilience to pathogen re-infestation in response to Brassica seed meal amendment. Acta Horticulturae. 1044:105-112. Interpretive Summary: Soil-borne disease management without chemical fumigants remains a major challenge for many crop production systems including tree fruits. Soil fumigation has been the primary means used for the control apple replant disease but impending modifications to existing regulations are likely to increase the cost of soil fumigation and/or restrict use of this disease control measure on certain sites. Brassicaceae seed meal amendments have been effective in controlling apple replant disease but require post-plant application of the fungicide mefenoxam. Therefore, a composite seed meal formulation was devised which included both yellow mustard (Brassica juncea) and white mustard (Sinapis alba) and examined for disease control in organic orchard systems. The composite seed meal formulation was as effective as soil fumigation in controlling replant disease and resulted in tree growth and yield that was equivalent to or greater than that attained in fumigated soils. The pre-plant seed meal amendment suppressed lesion nematode populations and root infection by Pythium spp. relative to the no-treatment control through three growing seasons while lesion nematode populations typically recovered in fumigated soil. Long-term suppression of plant pathogens in response to pre-plant SM amendment was associated with the persistence of a distinctive microbial community associated with apple roots. In contrast, the rapid re-colonization of fumigated soil by root pathogens was associated with the reversion of the rhizosphere soil microbial community to one that was indistinguishable from that of the no-treatment control. This difference in pathogen re-establishment typically corresponded with enhanced tree growth and yield in seed meal amended soils. Thus, it is plausible that the beneficial effects of Brassicaceae SM amendment in terms of overall growth and yield will be persistent leading to enhanced orchard economic viability.
Technical Abstract: Brassicaceae seed meal (SM) formulations were compared with pre-plant soil fumigation for the ability to control apple replant disease and to suppress pathogen/parasite re-infestation of orchard soils. Soil fumigation and SM treatments provided similar levels of disease control during the initial growing season. In controlled studies, SM amendment resulted in development of a soil system suppressive towards disease incited by Rhizoctonia solani AG-5 and Pythium abappressorium. In the field, SM treated soils exhibited resilience to re-infestation by Pratylenchus penetrans and Pythium spp. and correspondingly tree growth and yield was superior to that observed in fumigated soils. After two years, the rhizosphere microbiome in fumigated soils had reverted to one similar to that of the no-treatment control, while that from the SM treatment possessed unique bacterial and fungal profiles. Overall diversity of the microbiome was reduced in the SM treatment rhizosphere, suggesting that enhanced “biodiversity” was not instrumental in achieving system resilience and/or pathogen suppression.