Ouko, Jotham O. (1988) Influence of Different Cropping Systems, Plant Age and Varietal Differences on Incidence and Severity of Bacterial Pustule of Cowpea (ViNa Unguiculata (L.) Walp) Caused By Xanthomonas Campestris Pv. Vignicola (Burkholder) Dye. Masters thesis, University of Nairobi.
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Abstract
Cowpea bacterial pustule caused by Xanthomonas campestris pv. vignicola is one of the factors limiting cowpea production in Kenya especially in high rainfall areas. The present studies were undertaken to determine the effects of three different cropping systems and plant age on disease development and evaluate plant varietal reactions following inoculation with the pathogen. A preliminary attempt was also made to detect possible existence of pathogenic variation. The disease was found to have an incubation period of between seven and eight days when cowpea plants 21- 25 days old were foliar sprayed with a suspension o-f the pathogen. Disease spread within and between plants was shown to be least when cowpeas were grown as a relay crop after maize during the long rains and when grown as an intercrop with maize during the short rains. During the short rains disease incidence observed eight days after inoculation was 52.5% in cowpea-maize intercrop, 57.5% in cowpea pure culture and 57.0% in cowpea-maize relay crop. Forty days after inoculation this increased to 62.5%, 75.0% and 91.25% respectively. During the long rains disease incidence observed eight days after inoculation was 45.0% in cowpea-maize relay crop, 8.75% in cowpea pure culture and 5.0% in cowpea- maize intercrop which 16 days after inoculation increased to 68.75%, 100% and 100% respectively. Rainfall was observed to be important in disease development and spread as there was more disease and a faster rate of spread with increased amount of rainfall. Cowpea pure .culture and cowpea-maize intercrop planted during the long rains when about 748.9mm of rainfall was received had severe and faster disease spread compared to cowpea-maize relay crop.which had least disease and was on the ground when only 63.5mm of rain was received. Cowpea-maize relay crop during short rains had more disease and it was on the ground when the long rains started. During the experimental period there was no significant variation in relative humidity and daily temperatures between the treatments and hence they could not influence the differences observed in disease development and spread. Young plants were observed to have less disease than old plants when plants were inoculated at the same time but at different ages. During the short rains, plants 6, 4, 2 and 0 weeks old at inoculation had 100%, 82.5%, 60% and 0% disease incidence respectively 40 days after inoculation. However, there were no differences in disease development with increased rainfall. Disease severity also varied with age. Plants 6, 4, 2 and 0 weeks old attained severity scores of 4.5, 3.75, 2.5 and 1.0 during short rains and severity scores of 5.0, 5.0, 3.5 and 2.0 during long rains respectively. Varietal reactions to the pathogen varied but 5 varieties were found resistant, 14 moderately resistant while 4 were susceptible when grouped arbitrarily in mean disease severity classes where score 1-2.0 = resistant; 2.1-3.0 = moderately resistant; and 3.1-4.0 = susceptible. One of the 5 resistant varieties never developed any disease symptoms. Some variation was noted in the virulence of the 2 pathogen isolates tested on 22 cowpea varieties. The Mbita Point isolate was more virulent than the Mtwapa isolate.
| Item Type: | Thesis (Masters) |
|---|---|
| Subjects: | S Agriculture > SB Plant culture |
| Divisions: | Africana |
| Depositing User: | Geoffrey Obatsa |
| Date Deposited: | 27 Sep 2016 07:10 |
| Last Modified: | 27 Sep 2016 07:17 |
| URI: | http://thesisbank.jhia.ac.ke/id/eprint/1072 |
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