INCIDENCE, RACE DETERMINATION AND SURVIVAL OF BLACK ROT PATHOGEN (Xanthomonas Campestris pv campestris) IN Brassica SEEDS AND CROP DEBRIS IN KENYA

Abstract

Xanthomonas Campestris pv campestris (Xcc) is a seedborn pathogen that cause black rot, a destructive disease of Brassica and the primary source of inoculum. Xcc. is the major problem of infestation in Brassica seeds. Therefore imported and locally available seeds for production in Kenya were investigated for the presence of black rot and survival in Brassica debris. The objective of the research was to assess the incidence, survival and races of the pathogen in seed Brassica stock which are currently used for production in Kenya and survival of black rot in brasssica debris and race typing of the pathogen. The races found to be pathogenic to susceptible savoy cabbage Wirosa F1 were race type 1 and 3. The incidence and survival of black rot was conducted concurrently during the study at Kenya Plant Health Inspectorate Service Laboratories and National Agricultural Research Laboratories, Nairobi. The results show that Xcc is widespread in Brasssica seeds and survive in the Brasssica debris three months. Samples of cabbage, kale and collards seed were purchased from a variety of sources and locations in Kenya. Xcc infested cabbage and kale crop debris were collected from a smallholder’s farm and initially tested for the presence of the pathogen. The remains of the infested debris were left in the fields as farmers leftovers. They were collected at random for testing fortnightly for the presence of black rot for 6 months. The Xcc detected varied with respect to the types of Brassica, cultivar and seed source. The kales had the highest number of Xcc, followed by collards and cabbages. The type of Brassica sp (χ2 = (28.66), (5), cultivar (χ2 = (36.73), (17) and seed source (χ2 = (30.46), (11) influenced the Xcc detected. The Xcc detected was not influenced by collection region and origin of Brassica sp. The number of Xcc present in kale was slightly more than those found in cabbages. However there was no statistically significant difference on the number of Xcc present. The number of Xcc present in the debris depends on the existence of debris and the survival of bacteria decreases with increase in duration of exposure. The survival and existence of Xcc present in the soil was significant with time. The Xcc in the soil reduced with the length of time it is exposed. The Xcc race type 1 and 3 were obtained. The recommendations for the management of black rot is leaving the field without any brasssica or alternate hosts for about eight months and using certified seeds for multiplication