Yield loss assessment of silkworm production and development of disease management strategies against mulberry (Morus alba Linn.) red rust caused by Aecidium mori Barclay

The study was conducted to determine the effect of mulberry reel rust (MRR) on the yield and quality of mulberry leaves (cv. Batac), larval growth and development of silkworms, and the cocoon yield and quality of silk. It also aimed to evaluate some disease management interventions such as host resistance, sanitation, pruning and branch density management. Yield loss assessment showed that an average severity of 17.15% can cause a 7.4 reduction in yield from 10.05 t/ha to 9.305 t/ha in mulberry cv Batac. Tissue analyses of MRR-infected leaves revealed significant reduction in moisture content, total protein and vitamins. Moisture and protein content were found highest on leaves occupying the top portion of the branches. Sugar, starch, carotenoids, b-carotene and ascorbic acid did not vary significantly regardless of leaf position. The larval development, cocoon production and silk yield and quality were seriously affected when silkworm was fed with MRR-infected leaves. Silkworm larvae fed with MRR-infected leaves had high larval mortality and longer larval duration, was efficient feeder and produced lighter cocoons with silk filaments that frequently break during reeling. The number of cocoon per liter, percent reelable cocoon, cocoon shell percentage, denier, renditta and reelability were not affected by MRR. Disease management interventions such as host resistance and cultural practices such as sanitary pruning and branch thinning were evaluated under normal mulberry production systems. Field screening of 19 mulberry cultivars against MRR yielded one resistant cultivar (Alfonso), five moderately resistant (S13, C6, M. Local, S36, and SRDC2) and 13 susceptible cultivars. Component analysis of resistance showed that the resistant reaction conferred by resistant and moderately resistant cultivars was attributed to its ability to limit or suppress sporulation capacity, prolong latent period and shorten the infectious period of the fungus. Sanitation pruning, the cutting back of branches and total removal of remaining leaves significantly delayed the development of MRR, but such delay was not translated into an increase in mulberry yield. The increased in branch density to 12-15 branches per hill seemed to favor the epidemic development of MRR as shown by the significant increase in disease severity and area under disease progress curve (AUDPC) value. Despite the increase in MRR severity, the yield of mulberry was significantly increased due to greater number of productive branches.