SHORT COMMUNICATION - EVALUATION OF HOST-PATHOGEN INTERACTION OF MYCOVELLOSIELLA CAJAN WITH PIGEONPEA

Although Mycovellosiella cajan   is an important pathogen limiting production of pigeonpea through transmission of Mycovellosiella   leafspot, little is known about the structural formation of either the host (pigeonpea) or the fungus. Thus, this study was conducted to assess any differences in structure as an indication of resistance in pigeonpea genotypes to Mycovellosiella cajan. Germtube growth was not different in either of the pigeonpea germplasms assessed. Penetration in pigeonpea by Mycovellosiella cajan was inhibited by production of stomatal exudates in resistant varieties. In susceptible varieties germtube grew towards the stomata and penetrated either directly or through the stomata. In resistant varieties germtube bypassed the stomata and the point of penetration was not easily noticed. Mycovellosiella cajan sporulated in susceptible pigeonpea leaves 16 - 18 days after inoculation and in resistant varieties, conidiophores were not observed even after 16 days. In susceptible varieties there was rupturing of the stomata due to mass production of conidiophores through the stomata

Reaction of potato cultivars to Ralstonia solanacearum in Kenya

A survey of bacterial wilt (BW) incidence was carried out in three potato producing districts of Kenya, namely, Nyeri, Nyandarua, and Meru in 1997. The survey was carried out in 30 randomly selected farms in each district. Incidence of BW was highest (18.8%) in Nyeri district, intermediate (16.7%) in Meru and lowest (10.4%) in Nyandarua. A significant and negative correlation (P=0.05; r = -0.34) between bacterial wilt incidence and altitude was observed. Fifteen potato cultivars, Nyayo, Desiree CIP-800048, Roslin Tana, Kerrs pink LB-5, Golof (Dutch Robjin), B53, Tigoni CIP-381381.13, Rutuku CIP-720097, Asante CIP-381381.20, Kenya Dhamana CIP-800228, Mauritius Clone (89016), KP93739.26, KP92633.26, and Cruza148 CIP-72011 were subsequently evaluated for their reaction to Ralstonia solanacearum in artificial and natural infections in the greenhouse and in the field. Although none of the cultivars appeared resistant, there were significant (P=0.05) differences in bacterial wilt incidence and severity among the cultivars. Cultivars Kenya Dhamana, Mauritius and Cruza (CIP-720118) had low bacterial wilt severity and incidence and were rated tolerant, whereas the other cultivars were rated moderately susceptible or very susceptible. Key Words: Bacterial wilt, incidence, Kenya, Solanum tuberosum, tolerance (African Crop Science Journal 2001 9(1): 251-256

Studies on the interaction between Ralstonia solanacearum (Smith) and Meloidogyne Spp. in potato

A survey was undertaken to determine population density of Meloidogyne   juveniles (J2) in 90 fields randomly selected from three potato-producing districts in Kenya namely Nyeri, Meru and Nyandarua. Mean nematode densities were highest (45) in samples collected from Nyeri and Nyandarua and lowest (31) in soil samples collected from Meru. The reaction of 15 potato cultivars to Meloidogyne incognita   was determined under greenhouse conditions. Plants were inoculated with 6000 eggs and second-stage juveniles each. Highly significant (P=0.01) differences were observed between the cultivars. Galling index was highest (5.5) in cv. KP93739.26 and lowest (1.9) in cv. Nyayo. All cultivars supported nematode reproduction with the highest (5.0) egg mass index being recorded in cultivars KP93739.26, Kerr's Pink, Desiree CIP-800048, KP92633.26 and B53. No cultivar exhibited immunity. The relationship between infection by root-knot nematodes and severity of bacterial wilt in three potato cultivars with varying levels of resistance to bacterial wilt namely Asante CIP 381381.20 (susceptible), B53 (moderately susceptible), and Kenya Dhamana (resistant), was investigated in a greenhouse experiment. Bacterial wilt was more severe in plants infected with both pathogens as compared to plants infected with R. solanacearum   alone

Colonisation of resistant and susceptible bean tissues by Phaeoisariopsis griseola (Sacc) Ferr.

(African Crop Science Journal 1999 7(4): 523-530

Distribution of lesion nematodes associated with maize in Kenya and susceptibility of maize cultivars to Pratylenchus zeae

(African Crop Science Journal 1998 6(4): 367-376

The choice of grass species to combat desertification in semi-arid Kenyan rangelands is greatly influenced by their forage value for livestock

Livestock production is the main source of livelihood in the arid and semi-arid lands in Africa. However, desertification characterized by vegetation degradation and soil erosion is a major threat to the sustainability of land-based production systems. Native rangeland forage species Cenchrus ciliaris L. (Buffel grass/African foxtail grass), Eragrostis superba Peyr. (Maasai love grass) and Enteropogon macrostachyus (Hochst. Ex A. Rich.) Monro ex Benth. (Bush rye grass) have been used to combat desertification. The objectives of the study were to identify the best-suited native grass species to combat desertification in a semi-arid environment in Kenya and to identify the preferred grass species among the agropastoralists in the area. Percentage basal cover, plant densities and frequencies of the three grasses in pure stands and mixtures were estimated. Grass species preferences were through household survey and focus group discussion. Results showed a significant difference (P < 0 05) in plant densities and cover estimates: E. macrostachyus was ranked first; C. ciliaris and E. superba were ranked second and third respectively. The agropastoral farmers, however, preferred E. superba followed by C. ciliaris and E. macrostachyus, a reverse trend. These results suggest that the choice of grass species to combat desertification is influenced more by its contribution as a source of forage for livestock than its contribution for rehabilitation purposes