Survey of bacterial blight of coffee in Kenya and studies of kinetics of pseudomonas syringae, van hall in coffee foliage.

Abstract

A survey was conducted in the coffee growing areas of Kenya during the months of August, September, and October 1987 to determine the ecological distribution of bacterial blight of coffee and its incitant Pseudomonas syringae, Van Hall. The survey covered the three main coffee growing zones viz. upper middle zone 1 (UM1), upper middle zone 2 (UM2), which forms the main coffee growing zone and upper middle zone 3 (UM3) which is the marginal coffee zone. Three types of.Pseudomonads appeared consistently and relatively often and were categorized according to colony characteristics on nutrient Sucrose agar and 'biochemical:;physiological characteristic ics. The three groups were designated as Pseudomonas SPP 1, 2 and 3. Pseudomonas spp 3 was found to be non fluorescent and non pathogenic to coffee. Pseudomonas SPP-l was also found to be non pathogenic and was.characteristic of a saprophyte because of its fast growth and positive Arginine dehydrolase action. Further test showed that the species was Pseudomonas fluorescens, bio-type 1.

Pseudomonas SPP 2 was found to be Arginine dehydrogenase negative, was not a gelatin liquifier and was oxidase negative. These reactions suggested that Pseudomonas spp~was Pseudomonas syringae, Van Hall. This was in agreement with characteristics of Pseudomonas syringae, Van Hall reported earlier (Ramos and Shavdia 1976, Ramos, 1979). Pathogenic tests on various isolates of Pseudomonas SPP-2 showed that the isolates were all pathogenic to coffee. Eight isolates of Pseudomonas Spp~(Pseudomonas syringae, Van Hall) were isolated from eight widely separated geographical areas which were all found to fall in the marginal coffee areas (Upper middle zone- 3). No isolate with characteristics similar to Pseudomonas syringae was isolated from UM-l and UM-2. The spread of bacterial blight was found to be confined in certain areas of UM-3. The pathogen was isolated only in these areas. The growth patterns of Pseudomonas syringae, Van Hall in its natural host coffee (Coffea arabica L.) followed a typical bacterial growth curve. After inoculation by injection-infiltration method, the population of the bacteria initially increased rapidly, having a logarithmic phase running from the 1st day of inoculation to the 3rd day, transition 3rd - 5th day and

and finally the stationary phase where the bacteria population remained stable or declined slowly. Initial level of inoculum was found to influence the rate of growth and final population level achieved in the tissues. Kinetics of Pseudomonas syringae multiplication in the foliage of three varieties (SL-34, SL-28 and Catimor) showed that the rates of multiplication; final population, degree of colonization and severity of symptoms was highest in SL-28, lowest in Catimor and intermediate in SL-34. The reactions suggest that Catimor has the highest, SL-34 intermediate I and SL-28 the lowest resistance to bacterial blight of coffee. Pseudomonas syringae was found to multiply equally well in young and old leaves of coffee but at a lower rate in old leaves. However, the pathogen was found to multiply at faster rates and to higher final population in young leaves compared to old leaves. Symptoms assessment showed that old leaves were more resistant than young leaves. This observation i~ the greenhouse was found to be in agreement to the observations made in the field. Age resistance was found to be correlated to the apparent inability of the pathogen to multiply extensively in the old leaves. However, the pathogen was found to multiply

at similar rates and final populations in both the young and old leaf extracts. This work suggested that the differences in multiplication between the young and old leaves was not due to unfavorable nutrient status in the old leaves·