Plant parasitic nematodes associated with cabbage in different agro-ecological in Nyandarua and Embu counties, in Kenya

Abstract

Cabbage (Brassica oleracea L. Var. capitata) is an important vegetable crop in Kenya. It is widely used as human food and animal feed. Owing to findings that cabbage is a poor host to root knot nematode (RKN), this crop has been incorporated in plant parasitic nematode (PPN) management as a rotation crop. As a result very little has been done to study nematodes associated with this crop, yet there are reports of nematodes infecting it. A survey was therefore conducted in Nyandarua and Embu Agro-ecological Zones (AEZs), of Kenya to determine the types, abundance and frequency of occurrence of PPNs associated with. cabbage. A total of 60 soil and root samples were collected from six AEZs.

Nematodes were extracted from 100 g of soil per sample using the modified Baermann extraction tray technique while nematodes within the roots were extracted using modified maceration and filtration technique. Roots were rated for galling index using a scale of O-S, then stained for egg masses and presence of endoparasitic nematodes. Extracted nematodes were enumerated and identified to genera level. A total of nineteen (19) genera of PPNs belonging to ten (10) families of the Order Tylenchida, Dorylaimida and Triplonchida were identified from both soil and roots. Lesion nematodes (Pratylenchus spp.) were detected in S8% of the root samples, followed by Helicotylenchus spp. (27%) and root-knot nematode (RKN) Meloidogyne spp. (23%). The RKN galling index ranged from 1 to 2 on a scale of I-S. The lesion nematodes had the highest frequency of occurrence (A/F) in soil (87%) followed by Helicotylenchus spp. (82%) and Tylenchorhynchus spp. (67%). Other PPNs genera were identified at varying absolute frequencies. The population densities of nematodes differed significantly (P<O.OS) between AEZs.

The population density of PPNs recorded from cabbage roots in UHl b was significantly (P<O.OS) higher than all other AEZs. The highest nematode population in soil was recorded in UHla while UMI had the lowest for both root and soil samples. Various genera of PPN were found to differ (P<0.05) significantly. Pratylenchus spp. was present in a higher population density compared to other nematodes in both roots and soil, Helicotylenchus spp. and RKN were second in density in soil and root respectively. There was no significant difference (P>O.OS) between RKN galling index across AEZs. Soil physical-chemical properties, farmer practices and cabbage varieties cultivated may have significantly influenced occurrence and population densities of various PPN. Pathogenicity tests are necessary to determine the damages caused by nematodes reported herein. There is also need to screen various cabbage cultivars for resistance and tolerance to various PPNs.