|Crop Knowledge Master|
|reniform nematode on papaya (Plant Disease Pathogen)|
(In: Wayne Nishijimas papaya compendium)
The reniform nematode has an extensive host range. For more information on other hosts, please see the general summary on Rotylenchulus reniformis.
This summary focuses on the affects of the reniform nematode on papaya.
R. reniformis is one of the most widely distributed species and is of major global economic importance to agriculture.
The reniform nematode has been found to be the most important nematode pest of papaya. It is generally serious where the previous crop grown was pineapple.
Above-ground symptoms of plants infected by the reniform nematode are similar to those associated with one or more of the following conditions: 1) lack of proper nutrients, 2) chronic moisture stress, and/or 3) poor soil aeration. The above-ground symptoms appear as moderate to severe leaf chlorosis and plant stunting. Some wilting may occur during periods of peak transpirational stress on the plant. Below ground symptoms are not readily detectable by the untrained observer. However, reniform nematode presence on the roots may be observed with the aid of a 10x hand lens. The small sand-like bodies which remain attached, after the root system is carefully washed, are eggmasses of the nematode. Fruits produced are smaller than normal and may be slightly insipid.
The predominant reniform species found on papayas in most of the world is R. reniformis. Rotylenchulus parvus (Williams) Sher is reported on papayas in Kenya. Many commonly cultivated crops as well as weeds are hosts of the reniform nematodes. Because of their small size, they do not traverse distances of more than a few inches in their lifetime. Juveniles that hatch from eggs are less than 500 Ám long. After undergoing several molts, female juveniles become young adults and penetrate the root cortext and become sedentary. The portion of the body that remains outside the root enlarges and becomes kidney-shaped, hence the name "reniform." After maturation the female secrets a gelatinous substance around her body (the sand-like bodies referred to above) into which she lays about 100 eggs. A complete life cycle is possible in about 25 days. The reniform nematode feeds near the phloem in papaya roots inducing the formation of giant cells. These are centers of high metabolic activity that compete with other parts of the plant for food and nutrients. The nematode also may feed in the root cortex and cause mechanical breakdown of the cortical cells, thus providing suitable sites for attack by fungi.
Reniform nematodes are principally spread through cultivation and surface run-off or irrigation water.
Nematode-infested sites and infected seedlings should both be avoided when growing papayas. Former pineapple fields, especially, should be avoided.
Preplant soil fumigation has been used to reduce nematode populations, and have resulted in increased vigor and yields. No nematicides are registered for use on living papaya plants in the United States. Tests of some common systemic nematicides showed a positive growth response but have been phytotoxic to papayas.
Ayala, A., Acosta, N., and Adsuar, J. A. 1971. A preliminary report on the response of Carica papaya to foliar applications of two systemic nematicides. Nematropica 1:10 (Abstr.).
Cohn, E., and Duncan, L. W. 1990. Nematode parasites of subtropical and tropical fruit trees. Pages 347-362 in: Plant Parasitic Nematodes in Subtropical and Tropical Agriculture. M. Luc, R. A. Sikora, and J. Bridge, eds. CAB International, Wallingford, UK.
Hine, R. B., Holtzmann, O. V., and Raabe, R. D. 1965. Diseases of papaya (Carica papaya L.) in Hawaii. Hawaii Agric. Exp. Stn. Bull. 136, Univ. of Hawaii, 26 pp.
Lange, A. H. 1960. The effect of fumigation on the papaya replant problem in two Hawaiian soils. Proc. Amer. Hort. Soc. 75:305-312.
McSorley, R. 1981. Plant parasitic nematodes associated with tropical and subtropical fruits. Florida Agric. Exp. Stn. Bull. 823, Univ. of Florida, 49 pp.
Sivakumar, C. V., and Seshadri, A. R. 1972. Histopathology of infection by the reniform nematode, Rotylenchulus reniformis Linford and Oliveira, 1940 on castor, papaya and tomato. Indian J. Nematol. 2:173-181.