Etiology and prevalence of phytophthora foot rot of black pepper (Piper nigrum. L.) And reaction of some accessions to the disease in southwest Ethiopia

Abstract

Black pepper (Piper nigrum), an economically important species of the family Piperaceae, is a perennial glabrous woody climber that yields the ‘black pepper’ of commerce, which is profusely used as a culinary spice and condiment all over the world. It has been more than three decades since the crop is introduced to Ethiopia and currently its production is expanding in the southwestern part of the country. However, its cultivation has been under threat due to various diseases and insects. Several diseases caused by fungi, bacteria, virus and mycoplasma affect black pepper however, based on crop loss and disease distribution foot rot disease is considered as the major one. Although the disease is becoming a serious threat in cultivation of the crop, so far there is no research work done on Phytophthora foot rot in Ethiopia; moreover, the causal agents are not properly identified and the reactions of black pepper accessions to the disease are not known. The aim of this study was to assess and detect Phytophthora foot rot syndrome of black pepper and to isolate and identify its causal pathogen thereby determine the prevalence and importance of the disease. In the current study Survey was done in five wheredas; Bench, Guraferda, Yeki, Andracha and Godere using purposive stratified random sampling technique. Phytophthora isolates were identified by Etiology and by establishing pathogenecity. Thirteen accessions of black pepper were evaluated for their reaction to the pathogen in CRD with three replications. 105 sporangia/ml was used to inoculate three months old black pepper seedling. According to the survey the average maximum leaf infection index (LII) 16.7% was recorded in Benchmaji zone while least LII 9.2% was observed in Mejenger zone. Among the different places surveyed, maximum LII 18.24% was recorded at Benchmaji zone while the minimum (6.7%) LII was recorded from Sheka zone estate-farms. Maximum 26.87% foliar yellowing index (FYI) was observed at Sheka zone and least 21.2% FYI at Benchmaji zone of SNNPRS. The mean maximum Leaf defoliation index (LDI) 17.9%, collar infection index (CII) 18.9% and vine wilt index (VWI) 21.4% was recorded in Mejenger zone and mean minimum LDI (10.9%), CII (5.5%) and VWI (14.5%) were recorded in Sheka zone. The average percentage of FYI, LDI, VWI, LBI and CI for zones ranged from 58.5 to 70.8%, 20.8 to 35.8%, 25.2 to 35.8%, 53.2 to 77.2% and 13.3 to 35.8% respectively. Rainfall, number of rainy days and relative humidity, had a positive significant correlation with the disease severity whereas; temperature and sunshine hours had a significant negative correlation to disease development under natural condition. From the total of 167 fungal isolates Phytophthora species were the most abundant 107 isolates followed by Fusarium spp. and Phythium spp. The growth patterns of the isolates were cottony, rosaceous and stellet, with the occurrence of 50, 37, and 13% respectively. Colony growth rate (mm/day) of P. capsici isolate was found significantly different on different medium. Faster growth was found on PDA followed by TA and CA. The length breadth ratio of sporangia was ranged from 1.2 to 2.0 µm. According to the current investigation all P. capsici isolates included in the test were pathogenic on black pepper. Pathogen of foot rot of black pepper was characterized as P. capsici on the basis of Etiology and by establishing its pathogenicity on rooted cuttings. Hence, it was confirmed that currently, there are no commercial cultivars which are resistant to the disease in Ethiopia. So, we recommend that introducing tolerance varieties and evaluate some other means of diseases management will be important in order to mitigate the problem.