Resistance of Kenyan wheat germplasm to Fusarium head blight and deoxynivalenol contamination

Article PurchasedFusarium head blight (FHB) of wheat causes quantitative and qualitative reduction in yield. Cultivar resistance is the most effective method of managing the disease. This study evaluated the resistance of wheat germplasm currently available in Kenya to Fusarium head blight and deoxynivalenol (DON) contamination. Nine wheat varieties and four CIMMYT lines were evaluated for susceptibility to FHB under two diverse agro-ecologies in Nakuru and Narok Counties, Kenya during the 2013 cropping season and in the greenhouse. The varieties and lines were inoculated at mid-anthesis with mixed inocula of three isolates of F. graminearum. Incidence and severity of FHB were assessed weekly and data on severity used to calculate the area under disease progress curve (AUDPC). After harvest, incidence of F. graminearum in the grain was determined and DON contamination determined by direct competitive enzyme-linked immunosorbent assay (ELISA). Incidence and severity of FHB differed significantly (p ≤ 0.05) among the varieties and lines with variety Kwale showing the least disease while line 10155 had the highest FHB levels. The AUDPC ranged from 69.8 to 120.1 for the least and most susceptible varieties, respectively. All the wheat lines and varieties accumulated DON ranging from 442 to 748 ng/g (Mean = 572 ng/g). There was a positive correlation between FHB severity, AUDPC, re-isolation frequency of F. graminearum and DON accumulation. The assessed wheat varieties and lines could be grouped into two categories: moderately tolerant and susceptible. Wheat varieties and lines available in Kenya are susceptible to FHB and DON contamination implying need for considering other strategies for managing FHB

Effect of cropping systems on accumulation of Fusarium head blight of wheat Inocula in crop residues and soils

Article PurchasedFusarium head blight (FHB) is an economically important disease of wheat, which causes reduction in grain yield both quantitatively through reduced seed weight and qualitatively by contaminating grains with mycotoxins. The effect of cropping systems on accumulation of FHB inocula in crop residues and soil was assessed at hard dough stage of wheat during the 2013 cropping season in three agro-ecological zones in Narok County, Kenya. A semi structured questionnaire was used to obtain information on wheat production practices. Fusarium spp. were isolated from crop residues and top soil, while incidence and severity of FHB were assessed at mid-anthesis. Majority of the wheat farmers were small scale producers who rotated wheat with maize, grew the two crops in adjacent fields, grew wheat in consecutive years, left wheat residues as standing hay for livestock and practiced simple land preparation methods. Prevalence of FHB was 100%, while mean incidence and severity were 20.7 and 28.4%, respectively. The most frequently isolated Fusarium spp. were F. chlamydosporum and F. graminearum in crop residues and F. oxysporum and F. proliferatum in soil. The incidence of Fusarium spp. in soil and crop residues was highly correlated to FHB incidence but not to severity of the disease. Wheat production practices affect the survival of Fusarium spp. in soil and crop residues between cropping seasons. It is therefore, recommended that after harvesting, wheat straw and maize stover should be removed from the field or be incorporated into the soil through tillage to allow faster decomposition. Inclusion of maize as a rotation crop in wheat production should also be avoided

Occurrence of Fusarium head blight of wheat and associated mycotoxins in Narok and Nakuru Counties, Kenya

Open Access JournalFusarium head blight (FHB) is an important disease of small grain cereals. This study assessed the incidence and severity of FHB of wheat at hard dough stage, and levels of deoxynivalenol and T2-toxin at harvest by direct competitive enzyme linked immuno-sorbent assay. Wheat ears were randomly sampled from 51 farms in Narok County and 51 farms in Nakuru County at hard dough stage while wheat kernels were sampled at harvest. Prevalence of FHB in both Counties was 100%. The mean incidence of FHB was 28.4% and 20.5% in Narok and Nakuru Counties, respectively with 16.9% and 11.7% corresponding severity. Over 14 Fusarium spp. were isolated from wheat ears and kernels with F. avenaceum, F. poae and F. graminearum being isolated in the highest incidence. Levels of DON in the kernels ranged from below limit of detection (<LOD) to 623 µg/kg while the concentration of T-2 toxin ranged from <LOD to 69 µg/kg. The levels of DON and T2-toxin in wheat kernels in the two Counties were within the limits set by the European Commission and the United States Food and Drug Administration. The relatively low incidence and severity of FHB correlated with the low levels of DON and T-2 toxin in harvested wheat grains. There is however need to continuously monitor occurrence of FHB and toxin levels in wheat which varies among seasons due to variability in climatic conditions

Resistance and inheritance of common bacterial blight in yellow bean

Common bean ( Phaseolus vulgaris L.) is the most important food legume among the pulses. It is a cheap source of protein, especially in Sub-Saharan Africa. However, bean production is constrained by bacterial diseases, of which common bacterial blight ( Xanthomonas axonopodis p.v. phaseoli ) is prevalent in Africa. The objective of this study was to transfer resistance to common bacterial blight and determine its inheritance in yellow beans. Sources of resistance were CIAT lines, Wilk 2 and VAX 6, which were crossed with susceptible Lusaka yellow and Pembla. The parents, F1, F2 and backcross progenies were inoculated with X. axonopodis and the resulting blight severity determined. Quantitative traits, including days to flowering, number of pods, and seed yield were also determined. The F1 and backcrosses to the resistant parents were all resistant, while the F2 and backcrosses to the susceptible parents segregated in 3:1 and 1:1 ratios, respectively. Additive genetic effects were observed in quantitative traits like days to flowering, plant height, days to maturity and yield. Therefore, resistance to common bacterial blight is controlled by a single dominant gene. The resistant parents Wilk 2 and VAX 6 could be used to improve bean varieties that are susceptible to common bacterial blight.Le haricot commun ( Phaseolus vulgaris L.) est une nourriture la plus importante parmi les l\ue9gumineuses. C\u2019est une source moins ch\ue8re de prot\ue9ines, sp\ue9cialement en Afrique sub-Saharienne. Cependant, la production du haricot est handicap\ue9e par des maladies bact\ue9riennes, parmi lesquelles le fl\ue9trissement bact\ue9rien courant ( Xanthomonas axonopodis p.v. phaseoli ) qui est le plus prevalent en Afrique. L\u2019objectif de cette \ue9tude \ue9tait de transf\ue9rer la r\ue9sistance au fl\ue9trissement bact\ue9rien et de d\ue9terminer son h\ue9r\ue9dit\ue9 dans les haricots jaunes. Les sources de r\ue9sistance \ue9taient lign\ue9es CIAT, Wilk 2 et VAX 6, qui \ue9taient crois\ue9es avec le susceptible Lusaka jaune et Pembla. Les parents F1, F2 et les prog\ue9nies de croisement en retour \ue9taient inocul\ue9es avec X. axonopodis et le degr\ue9 de s\ue9v\ue9rit\ue9 du fl\ue9trissement d\ue9termin\ue9. Des traits quantitatifs, incluant les jours \ue0 la floraison, le nombre de gousses et le rendement en grains \ue9taient aussi d\ue9termin\ue9s. Les F1 et les produits de croisements en retour des parents r\ue9sistants \ue9taient tous r\ue9sistants, alors que les F2 et les produits de croisements en retour des parents susceptibles \ue9taient s\ue9gr\ue9gu\ue9s dans les rapports 3:1 et 1:1, respectivement. Des effects g\ue9n\ue9tiques additifs \ue9taient observ\ue9s dans les traits quantitatifs tels que les jours \ue0 la floraison, la hauteur des plants, les jours \ue0 la maturit\ue9 et le rendement. Ainsi, la r\ue9sistance au fl\ue9trissement bact\ue9rien est controll\ue9 par un seul g\ue8ne dominant. Les parents r\ue9sistants Wilk 2 et VAX 6 pourraient \ueatre utilis\ue9s pour am\ue9liorer les vari\ue9t\ue9s de haricot susceptibles au fl\ue9trissement bact\ue9rien commun

Inheritance of resistance to angular leaf spot in yellow beans

Angular leaf spot ( Phaeoisariopsis griseola (Sacc) is an important disease of common bean ( Phaseolus vulgaris L.) in most parts of Africa, causing yield losses of 40-80%. This study was carried out to determine the inheritance of resistance to angular leaf spot in yellow beans. Biparental crosses were done between susceptible yellow bean genotypes and angular leaf spot resistant parents to generate F1, F2 and backcrosses. Resistance was evaluated in a screen house and field after inoculation with Phaeoisariopsis griseola. The F1 were resistant, indicating that resistance was dominant. There was no significant deviation from the expected 3:1 ratio for resistant to susceptible in the F2 population, confirming that resistance to angular leaf spot was both monogenic and dominant. The backcross to Lusaka Yellow showed a 1:1 segregation ratio, while the backcrosses to Mexico 54 were all resistant. Pembela was susceptible to angular leaf spot, while the F1 were resistant. The ratio of 3:1 represents resistant : susceptible F2 populations. All backcrosses to Mexico 54 were resistant, confirming that resistance to angular leaf spot in Mexico 54 is controlled by a single dominant gene. The results of the study showed that resistance to angular leaf spot in yellow beans is governed by a single dominant gene. This can be used to improve the local landraces by incorporating angular leaf spot resistance and high yield traits.La t\ue2che agulaire des feuilles ( Phaeoisariopsis griseola (Sacc) est une maladie importante du haricot commun ( Phaseolus vulgaris L.) dans la plus part de regions africaines, causant des pertes de rendement d\u2019environ 4080%. Cette \ue9tude \ue9tait conduite pour d\ue9terminer l\u2019acquisition de la r\ue9sistance des haricots jaunes \ue0 la maladie de t\ue2che angulaire. Les croisements biparentaux \ue9taient effectu\ue9s entre les g\ue9notypes du haricot jaune susceptible et les parents r\ue9sistants \ue0 la g\ue9n\ue9ration F1, F2 ainsi que de croisements r\ue9currents. La r\ue9sistance \ue9tait \ue9valu\ue9e en serre et au champ apr\ue8s inoculation avec Phaeoisariopsis griseola. Les F1 \ue9taient r\ue9sistantes, indicant que la r\ue9sistance \ue9tait dominante. Il n\u2019avait aucune d\ue9viation significative du rapport attendu 3:1 pour la r\ue9sistance, au susceptible dans les populations F2, confirmant que la r\ue9sistance \ue0 la t\ue2che angulaire de feuilles \ue9tait monog\ue9nique et dominant. Les produits du croisement en retour de Lusaka Yellow a montr\ue9 un rapport de s\ue9gr\ue9gation 1:1, pendant que ceux de Mexico 54 \ue9taient tous r\ue9sistants. Pempela \ue9tait susceptible \ue0 la t\ue2che angulaire, alors que les F1 \ue9taient r\ue9sistantes. Les prog\ue9nies F2 s\ue9gr\ue9g\ue9es en un rapport 3:1 pour r\ue9sistant au susceptible et le backcross (croisement en retour) au Pempela avait donn\ue9 un rapport 1:1 pour r\ue9sistant au susceptible. Tous les produits du croisement en retour du Mexico 54 \ue9taient r\ue9sistants, confirmant que la r\ue9sistance \ue0 la t\ue2che angulaire des feuilles dans Mexico 54 est controll\ue9e par un seul g\ue8ne dominant. Les r\ue9sultats de cette \ue9tude ont montr\ue9 que la r\ue9sistance \ue0 la t\ue2che angulaire dans les haricots jaunes est gouvern\ue9e par un seul g\ue8ne dominant. Ceci peut \ueatre utilis\ue9 pour am\ue9liorer les vari\ue9t\ue9s locales indig\ue8nes par incorporation de la r\ue9sistance \ue0 la t\ue2che angulaire des feuilles et les traits \ue0 rendement \ue9lev\ue9

Control of Bean Rust using Antibiotics Produced by Bacillus and Streptomyces species - Translocation and Persistence in Snap Beans

Antibiotic culture filtrates produced by Bacillus (CA5) and Streptomyces spp. were tested for translocation and persistence when applied on snap beans inoculated with rust ( Uromyces appendiculatus ) in greenhouse pot experiments. The antibiotics were applied on the first trifoliate leaves and translocation was assessed as the number of rust pustules on non-treated leaflets or trifoliates while persistence was assessed as the number of rust pustules on rust infected plants at different times after antibiotic treatment. The treatments were replicated three times, each replicate consisting of a pot containing three plants. Antibiotics from both Bacillus and Streptomyces were found to have up to 100% trans-lamina and leaflet-to-leaflet translocation but no significant trifoliate-totrifoliate translocation. The antibiotic culture filtrates also retained significant rust control for up to 10 days after application on the bean plant. However, no significant rust control was found on the plants after 16 days of treatment. The study indicated that the antibiotics produced by antagonistic Bacillus and Streptomyces species possess systemic activity that can persist within the plant for over one week. These metabolites are potential bean rust control products that could be incorporated in integrated disease management program

Seasonal dynamics and alternate hosts of thrips transmitted Iris yellow spot virus in Kenya

Thrips-transmitted Iris yellow spot virus (IYSV) (Family Tospoviridae, Genus Orthotospovirus) is a major constraint to onion ( Allium cepa L.) production in Kenya. Determining seasonal patterns of the vector and alternate hosts of the virus could help onion farmers plan Integrated Pest Management strategies; while allowing them to move away from calendar-based applications of insecticides. The objective of this study was to determine the distribution, seasonal variations and alternate hosts of vector and IYSV. For distribution, a survey was carried out on a network of farms in all onion growing areas in Kenya; while for seasonality, surveys were done in two areas; Loitoktok and Naivasha. Data were collected on IYSV incidence, thrips population and alternate hosts. Results showed IYSV was widely distributed in all onion growing areas; with incidence varying from 26 to 72%. Highest IYSV incidence was recorded during the cool-dry season, and varied from 56.5 to 71%; while lowest IYSV incidence in onions was observed during the cool and wet season (29.9 to 32.2%). Iris yellow spot disease incidence positively correlated with the number of onion thrips in Loitokitok (r = 0.659; P&lt;0.0001) and Naivasha (r = 0.623; P&lt;0.0001). Identified alternate hosts for IYSV were leeks, chives, shallots, lambsquarters, redroot pigweed, Chinese lantern and black nightshade.Occurrence of thrips on onions, which is grown all year round calls for urgent integrated pest management strategies that includes host plant resistance, field sanitation, forecasting and use of beneficial insects and parasitoids to reduce impact of the pest and disease. Plant health adherence through removal of alternate weeds hosts around the cultivated fields, would be useful in minimising IYSV incidence.Le virus Iris de la tache jaune (IYSV) transmis par les thrips (Famille Tospoviridae, Genre Orthotospovirus) est une contrainte majeure de la production de l\u2019oignon ( Allium cepa L) au Kenya. D\ue9terminer la distribution saisonni\ue8re du vecteur et les h\uf4tes alternatives des virus pourrait aider les producteurs d\u2019oignon \ue0 mettre en place des strat\ue9gies de gestion int\ue9gr\ue9e des pestes, en vue de leur permettre d\u2019\ue9viter les applications des insecticides sur la base du calendrier. L\u2019objectif de cette \ue9tude \ue9tait de d\ue9terminer la distribution, les variations saisonni\ue8res et les h\uf4tes alternatives du vecteur et de IYSV. Pour la distribution, une enqu\ueate a \ue9t\ue9 conduite sur un r\ue9seau de champs dans toutes les zones productrices d\u2019oignon du Kenya\ua0; alors que pour la saisonnalit\ue9, des enqu\ueates ont \ue9t\ue9 conduites dans deux zones\ua0; Loitoktok et Naivasha. Les donn\ue9es ont \ue9t\ue9 collect\ue9es sur l\u2019incidence d\u2019IYSV, la population de thrips et les h\uf4tes alternatives. Les r\ue9sultats ont montr\ue9 que IYSV \ue9tait largement distribu\ue9 dans toutes les zones de production d\u2019oignon\ua0; avec l\u2019incidence variant de 26 \ue0 72%. La plus grande incidence d\u2019IYSV a \ue9t\ue9 obtenue pendant la saison s\ue8che et froide, et varie de 56,5 \ue0 71% alors que la plus faible incidence de l\u2019IYSV sur les oignons a \ue9t\ue9 observ\ue9e pendant la saison humide et froide (29,9 \ue0 32,2%). L\u2019incidence de la maladie de la tache jaune de Iris \ue9tait positivement corr\ue9l\ue9e avec le nombre de thrips des oignons \ue0 Loitokitok (r = 0,659; P&lt;0,0001) et Naivasha (r = 0,623; P&lt;0,0001). Les h\uf4tes alternatives identifi\ue9es pour l\u2019IYSV \ue9taient des poireaux, les ciboulettes, les \ue9chalotes, les ambsquarters, les amarantes \ue0 racine rouge, la lanterne chinoise et la morelle noire. L\u2019occurrence des thrips des oignons produits toute l\u2019ann\ue9e appelle \ue0 des strat\ue9gies urgentes de gestion int\ue9gr\ue9e des pestes qui comprennent la r\ue9sistance de la plante h\uf4te, l\u2019assainissement du champ, pr\ue9vision, et l\u2019usage des insectes b\ue9n\ue9fiques et parasito\uefdes pour r\ue9duire l\u2019impact de la peste et de la maladie. Le respect de la sant\ue9 de la plante \ue0 travers l\u2019enl\ue8vement des adventices, les h\uf4tes alternatives dans les champs cultiv\ue9s, serait b\ue9n\ue9fique en minimisant l\u2019incidence de l\u2019IYSV

Multiple disease resistance in snap bean genotypes in Kenya

Snap bean ( Phaseolus vulgaris L.) is an important export vegetable crop, produced mainly by small to medium scale farmers under various disease constraints. Disease resistant varieties can reduce reliance on fungicides, and enhance the capacities of smallholder farmers to meet the stringent European export requirements for allowable fungicide residues. This study was carried out to identify snap bean lines with multiple disease resistance to angular leaf spot ( Phaeoisareopsis griseola ), anthracnose ( Collectotrichum lindemuthianum ) and rust ( Uromyces appendiculatus ). Seven groups of snap bean populations of different generations, and 45 bush snap bean lines, including local checks, were evaluated for resistance to the three diseases at two locations in Kenya. The disease with the highest severity was rust, followed by angular leaf spot. Among the advanced lines, two bush lines (KSB 10 W and KSB 10 BR), and one climbing line (HAV 130) had consistent multiple resistance to angular leaf spot, anthracnose and rust at both locations. Nine lines and 674 single plants were selected from populations showing multiple disease resistance. Resistance in selected lines reduced angular leaf spot, anthracnose and rust severity by 17, 16 and 36%, respectively. The multiple disease resistant lines were not the highest yielders but had the highest number of pods per plant. Climbing snap bean lines had thick pods that could reduce pod quality.Le haricot vert ( Phaseolus vulgaris L.) est une importante l\ue9gume d\u2019exportation, produite principalement par de petits fermiers sous diff\ue9rentes contraintes de maladies. Des vari\ue9t\ue9s r\ue9sistantes aux maladies peuvent r\ue9duire l\u2019utilisation de fongicides, et promouvoir la capacit\ue9 des petits fermiers \ue0 satisfaire les exigencies rigoureuses des exportations europ\ue9ennes en r\ue9sidus acceptables de fongicides. Cette \ue9tude \ue9tait m\ue9n\ue9e afin d\u2019identifier des lign\ue9es de haricots verts avec multiple r\ue9sistance \ue0 la t\ue2che angulaire des feuilles ( Phaeoisareopsis griseola ), \ue0 l\u2019anthracnose ( Collectotrichum lindemuthianum ) et \ue0 la rouille ( Uromyces appendiculatus ). Sept groupes de populations de diff\ue9rentes g\ue9n\ue9rations, et 45 lign\ue9es de haricots verts nains incluant les t\ue9moins locaux, \ue9taient \ue9valu\ue9s pour r\ue9sistance aux trois maladies dans deux localisations au Kenya. La maladie avec une s\ue9v\ue9rit\ue9 la plus \ue9lev\ue9e \ue9tait la roulle, suivie par la t\ue2che angulaire des feuilles. Parmi les lign\ue9es avanc\ue9es, deux lign\ue9es naines (KSB 10 W et KSB 10 BR), et une volubile (HAV 130) avaient une resistance multiple consistante \ue0 la t\ue2che angulaire des feuilles, \ue0 l\u2019anthracnose et \ue0 la rouille dans toutes les deux localisations. Neuf lign\ue9es et 674 plantes simples s\ue9lectionnn\ue9es des populations avaient montr\ue9 une r\ue9sistance multiple aux maladies. La r\ue9sistance dans les lign\ue9es s\ue9lectionn\ue9es avaient r\ue9duit la s\ue9verit\ue9 de la t\ue2che angulaire des feuilles, de l\u2019anthracnose et de la rouille de 17, 16 et 36%, respectivement. Les lign\ue9es de r\ue9sistance multiple n\u2019avaient pas des rendements plus \ue9lev\ue9s mais avaient un nombre plus \ue9lev\ue9 de gousses par plante. Les lign\ue9es de haricots verts volubiles avaient des gousses \ue9paisses susceptibles \ue0 r\ue9duire la qualit\ue9 de gousses

Control of Carnation Fusarium Wilt Using Antibiotics Culture Filtrate from Streptomyces Spp.

Streptomyces spp. isolated from soils collected from Kabete, Department of Crop Science, University of Nairobi isolates were screened for antibiosis against Fusarium oxysporum f. sp. dianthi in vitro. The culture filtrate of isolate 21, one of the antagonistic isolates was tested for activity and found to suppress growth of F. oxysporum f.sp dianthi in vitro. The culture filtrate was used to treat pathogen inoculated carnation cuttings and it reduced stem discolouration by 62.2% which was comparable to reduction by benlate that reduced stem discolouration by 78.3%. Different concentration levels of the culture filtrate (concentrated filtrate, normal filtrate, half strength filtrate and quarter strength filtrate) all effectively reduced discolouration of the carnation stems by 93.3, 73.1, 68.5 and 63.4%, respectively. Phytotoxicity that led to chlorosis and partial wilting during the first week of treatment was detected in the antibiotic treated plants especially when applied to young and tender cuttings. The chlorosis and partial wilting were significantly reduced when older and well established cuttings were used and when the culture filtrate was diluted to half or quarter strength

Control of Carnation Fusarium Wilt Using Antibiotics Culture Filtrate from Streptomyces Spp.

Streptomyces spp. isolated from soils collected from Kabete, Department of Crop Science, University of Nairobi isolates were screened for antibiosis against Fusarium oxysporum f. sp. dianthi in vitro. The culture filtrate of isolate 21, one of the antagonistic isolates was tested for activity and found to suppress growth of F. oxysporum f.sp dianthi in vitro. The culture filtrate was used to treat pathogen inoculated carnation cuttings and it reduced stem discolouration by 62.2% which was comparable to reduction by benlate that reduced stem discolouration by 78.3%. Different concentration levels of the culture filtrate (concentrated filtrate, normal filtrate, half strength filtrate and quarter strength filtrate) all effectively reduced discolouration of the carnation stems by 93.3, 73.1, 68.5 and 63.4%, respectively. Phytotoxicity that led to chlorosis and partial wilting during the first week of treatment was detected in the antibiotic treated plants especially when applied to young and tender cuttings. The chlorosis and partial wilting were significantly reduced when older and well established cuttings were used and when the culture filtrate was diluted to half or quarter strength