Pathogenicity of root-knot nematode (Meloidogyne incognita) on sweet potato (Ipomoea batatas L.) - IJAAR
- O.S. Osunlola*, B. Fawole
Root-knot nematode, Meloidogyne incognita, is a major biotic factor militating against sweet potato production. The pathogenicity of M. incognito on three sweet potato cultivars: Kayode, TIS 4400-2 and TIS 70357-OP-1-79 was investigated in a screen house experiment at the Department of Crop Protection and Environmental Biology, University of Ibadan, Ibadan, Nigeria. A vine cutting of each cultivar was planted in a 16 litre polyethylene pot containing 15 litre steam-sterilized sandy loam soil.
Three weeks after planting, the seedlings were inoculated separately at four inoculum densities: 0, 30,000, 60,000 and 90,000 eggs of M. incognito using a 3 x 4 factorial experiment replicated four times in a randomized complete block design. Data were collected on fresh shoot weight, fresh root weight, dry shoot weight, dry root weight, galling index, tuber yield, tuber quality and nematode reproduction.
All data were analyzed using ANOVA (p<0.05). M. incognita significantly (p<0.05) reduced the fresh shoot weight by 16.3-23.6%, fresh root weight by 28.3-62.3%, number of tubers by 63.2-69.2% and tuber yield by 72.3-83.2%. The
gall index and the final nematode population increased with increase in
inoculum density. The result showed that M incognita caused growth,
yield and quality reduction in sweet potato; therefore, management of
root-knot nematode should be part of sweet potato production efforts
especially in areas where the nematode is endemic.
Introduction
Sweetpotato is a dicotyledous plant that belongs to the family Convolvulaceae.. It originated from Central America and the North Western part of South America from where it was introduced to Europe by Columbus and to Asia, Africa and North America by Spanish and Portuguese explorers and traders (Onwueme and Charles, 1994). Currently, sweetpotato is grown throughout the tropical and sub-tropical world and in the warmer parts of the temperate countries and it forms an important part of the diet of these communities (Lenne, 1991). It is cultivated for its large, starchy, and sweet tasting tuberous roots. In addition, the young leaves and shoots are sometimes consumed as a vegetable (Woolfe, 1992; Odebode, 2008). Sweetpotato tubers are rich in carbohydrates, vitamins A and C, thiamine, niacin, riboflavin and also contains significant amounts of calcium and iron (Onwueme and Charles, 1994).
The increased consumption of sweetpotato is one important strategy for preventing vitamin A deficiency, especially among women and children (Odebode, 2008). It is consumed boiled, baked, roasted, or fried. Fresh tubers may also be fed directly to livestock or processed into flour which may be added to wheat flour for bread making (Onwueme and Charles, 1994; Odebode, 2008). Other processed products from sweetpotato include starch, alcohol, syrups, acetone, pectin, acetic acid, dyes, noodles, candy, desserts, and jam (Chivinge, et al., 2000; Odebode, 2008).
Losses caused by plant-parasitic nematodes to sweetpotato production around the world were estimated to 10.7% in 1987 causing losses of at least 2.6 billion US dollars (Sasser and Freckman, 1987). The root-knot nematodes (Meloidogyne spp) are considered to be the most important nematode in the production of sweetpotato (Oversweet, 2009). Root- knot nematode symptoms on sweetpotato include round to spindled shaped swellings (galls) on fibrous roots and cracks on fleshy storage roots (Lawrence et al., 1986). M. incognita has been implicated in yield reduction of sweetpotato by earlier workers. Gapasin and Validez (1979) reported a yield loss of 47.7% while Theberge (1985) recorded a yield reduction of 20- 30 % in his study. In the Philippines, losses of 50% have been recorded but it could lead to a total loss with three continuous cultivation in M. incognita-infested soil (Gapasin, 1984; 1986).In North Carolina,root-knot nematode was reported to cause yield loss of 6% in 1991. Information on effects of nematode on sweetpotato is very rare or scanty in Nigeria, therefore, this study was undertaken to evaluate the effect of M. incognita on the growth, yield and quality of sweetpotato cultivars commonly grown in Nigeria.
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