STATUS OF ARTHROPOD PESTS AND DISEASES OF CASSAVA: SCREENING FOR RESISTANCE TO CASSAVA RED SPIDER MITE AND WITCHES’ BROOM IN THE PHILIPPINES

The long production cycle of 6 months to one year allows cassava to be exposed to attack of pests and diseases. Like any other commercially-grown crops, cassava production is beset with many pests and diseases problems which contribute to low productivity caused by high losses either in terms of root yield or in root quality. Damage done by pests and diseases is one of the reasons why yield of even high-yielding varieties is not achieved.

A number of mites and insect pests and diseases attack cassava in the Philippines. In the late 80s, there were 3 mites, 3 scale insects, 3 mealybugs, 2 whiteflies, corn silk beetle, cerambycid beetle, leaf folder and mound-building termite infesting cassava (Villacarlos and Vasquez, 1989). For the diseases, fungal (Cercospora brown leaf spot and Cercospora leaf blight and cassava white leaf spot), cassava bacterial blight, cassava bacterial leaf spot and a number of postharvest diseases (Baniqued and Sajise, 1989).  

Based on survey in 2011-2015 conducted all over the country, new emerging diseases and pests were observed, namely: the cassava witches’ broom, bud necrosis, two mealybug species (the papaya and pink mealybug) and a mussel scale. The cassava red spider mite (RSM), Tetranychus kanzawai Kishida, and the cassava witches’ broom (CWB) caused by phytoplasma are considered the major constraints in cassava production (Vasquez 2016).  Both can reduce significant yield loss between 20-50% and significant reduction in starch content when infestation/infection coincides during the most susceptible stage of plant growth, i.e. first 3-4 months from planting.

            Since cassava is a long season crop, the most reliable and easy-to-adopt method among the control measures is the use of resistant cassava genotypes. Host plant resistance offers the most economical, sustainable and environmentally-sound means of controlling arthropod pests. Cassava resistance to pests and diseases in the Philippines has not been systematically studied. The only one studied so far was on screening of germplasm collections, advance lines and few varieties as one of the components of the breeding program in 1987-1992 for resistance to RSM and the white peach scale (Bacusmo et al., 1993). Since then no screening for resistance to pests and diseases been done at PhilRootcrops not until 2014 with the funding from the Department of Agriculture- Bureau of Agricultural Research.

The ongoing studies on pest and disease resistance conducted by PhilRootcrops focus on two major pest problems, CWB and RSM on 48 NSIC-registered varieties. Progress in the screening for mite resistance resulted in the selection of 7 tolerant and 4 moderately resistant varieties. For CWB, 6 high yielding varieties and tolerant varieties are identified. Three varieties are tolerant to both major pest problems. The basis for selection of varieties with potential resistance is not only based on the damage and symptom in the plant but also on growth and  yield parameters including dry matter and starch content.

Contact: Dr. Erlinda Vasquez: lindvasq@yahoo.com

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