PREVALENCE OF ANGULAR LEAF SPOT DISEASE AND SOURCES OF RESISTANCE IN COMMON BEAN IN EASTERN DEMOCRATIC REPUBLIC OF CONGO

Angular leaf spot ( Pseudocercospora griseola Crous U, Brown) is one of the most important diseases hindering common bean ( Phaseolus vulgaris L.) production in the Great Lakes Region of Africa, including the Democratic Republic of Congo. The disease causes extreme yield losses, estimated at 384.2 tonnes per year, in Sub-Saharan Africa. Little is known about the distribution, severity and incidence of the disease and the effect of agronomic practices and environmental factors on the disease prevalence in the country to facilitate interventions. A field survey was conducted during two crop seasons, February to June and September to January, in two main beans growing zones of eastern DRC namely; sub-humid highland and sub-humid mid altitude at low latitudes, in South and North Kivu, respectively. Severity and incidence of angular leaf-spot and other occurring diseases were assessed on common bean plants in farmers\u2019 fields. Angular leaf spot in these fields had an average severity index (PSI) of 49.9%. PSI was significantly different (P<0.05) between districts and seasons. Using multiple regression analysis, independent variables: growth stage, cropping system, districts and altitude were shown to have significant influence on the observed PSI (P<0.05) with R2 = 96.2%. The highest severity (PSI=59.7%) was observed in Kabare district, and the lowest in Uvira district (PSI=39.5%). Screening of a set of 37 released common bean varieties in DRC using virulent Andean and Mesoamerican isolates identified four resistant bean varieties; ARA 4, COD MLV 059, MLV 224/94B, LSA 144 and Mexico 54. Some of these varieties possess useful traits, in addition to acceptable seed market class, and are hence recommended as suitable parents for ALS resistant variety development and promotion in ALS prone environments.La tache angulaire ( Pseudocercospora griseola Crous U, Brown) est l\u2019une des maladies les plus importantes qui entravent la production de haricot commun ( Phaseolus vulgaris L.) dans la r\ue9gion des Grands Lacs d\u2019Afrique, y compris la R\ue9publique D\ue9mocratique du Congo. La maladie provoque des pertes de rendement extr\ueames, estim\ue9es \ue0 384.2 tonnes par an en Afrique Sub-Saharienne. Ily a encore peu de connaissance sur la distribution, la gravit\ue9 et l\u2019incidence de la maladie et l\u2019effet des pratiques agronomiques et des facteurs environnement aux sur la pr\ue9valence de la maladie dans le pays pour faciliter les interventions. Une enqu\ueatesur le terrain a \ue9t\ue9men\ue9e pendant deux saisons de r\ue9colte, de F\ue9vrier \ue0 Juin et de Septembre \ue0 janvier, dans deux zones principals de culture de haricots de l\u2019est de la RDC, \ue0 savoir: Sous-humides de haute altitude et sous-humides \ue0 basse altitude, au Sud et au Nord-Kivu. La gravit\ue9 et l\u2019incidence de la tache angulaire des feuilles et d\u2019autres maladies ont \ue9t\ue9 \ue9valu\ue9es sur les plants de haricots dans les champs des agriculteurs. Ces champs \ue9taient infest\ue9s par la maladie, avec unindice de gravit\ue9 moyen (IPS) de 49.9%. PSI \ue9tait significativement diff\ue9rent (P <0.05) entre districts et saisons. En utilisant l\u2019analyse de r\ue9gression multiple, les variables ind\ue9pendantes: stade de croissance, syst\ue8me de culture, districts et altitude ont montr\ue9 une influence significative sur le PSI observ\ue9 (P <0.05) avec R2 = 96.2%. La s\ue9v\ue9rit\ue9 plus \ue9lev\ue9e (PSI = 59.7%) a \ue9t\ue9 observ\ue9e dans le district de Kabare et la plus faible dans le district d\u2019Uvira (PSI = 39,5%). La s\ue9lection d\u2019un lot de 37 vari\ue9t\ue9s de haricot distribu\ue9es en RDC utilisant des isolats virulents Andins et M\ue9soam\ue9ricains a permis d\u2019identifier quatre vari\ue9t\ue9s de haricots r\ue9sistants; ARA 4, COD MLV 059, MLV 224 / 94B, LSA 144 et Mexique 54. Certaines de ces vari\ue9t\ue9s pr\ue9sentent des traits utiles en plus de son acceptabilit\ue9 sur lemarch\ue9 des semences, et sont donc recommand\ue9s comme des parents appropri\ue9s pour le d\ue9veloppement et la promotion des vari\ue9t\ue9s r\ue9sistantes ALS

A review of angular leaf spot resistance in common bean.

Angular leaf spot (ALS), caused by Pseudocer-cospora griseola, is one of the most devastating diseases of common bean (Phaseolus vulgarisL.) in tropical and subtropical production areas. Breeding for ALS resistance is difficult due to the extensive virulence diversity of P. griseolaand the recurrent appearance of new virulent races. Five major loci, Phg-1 to Phg-5, confer-ring ALS resistance have been named, and markers tightly linked to these loci have been reported. Quantitative trait loci (QTLs) have also been described, but the validation of some QTLs is still pending. The Phg-1, Phg-4, and Phg-5loci are from common bean cultivars of the Andean gene pool, whereas Phg-2 and Phg-3are from beans of the Mesoamerican gene pool. The reference genome of common bean and high-throughput sequencing technologies are enabling the development of molecular markers closely linked to the Phg loci, more accurate mapping of the resistance loci, and the compar-ison of their genomic positions. The objective of this report is to provide a comprehensive review of ALS resistance in common bean. Further-more, we are reporting three case studies of ALS resistance breeding in Latin America and Africa. This review will serve as a reference for future resistance mapping studies and as a guide for the selection of resistance loci in breeding programs aiming to develop common bean cultivars with durable ALS resistance

Prevalence of angular leaf spot disease and sources of resistance in common bean in eastern democratic republic of Congo

Angular leaf spot (Pseudocercospora griseola Crous U, Brown) is one of the most important diseases hindering common bean (Phaseolus vulgaris L.) production in the Great Lakes Region of Africa, including the Democratic Republic of Congo. The disease causes extreme yield losses, estimated at 384.2 tonnes per year, in Sub-Saharan Africa. Little is known about the distribution, severity and incidence of the disease and the effect of agronomic practices and environmental factors on the disease prevalence in the country to facilitate interventions. A field survey was conducted during two crop seasons, February to June and September to January, in two main beans growing zones of eastern DRC namely; sub-humid highland and sub-humid mid altitude at low latitudes, in South and North Kivu, respectively. Severity and incidence of angular leaf-spot and other occurring diseases were assessed on common bean plants in farmers’ fields. Angular leaf spot in these fields had an average severity index (PSI) of 49.9%. PSI was significantly different (P<0.05) between districts and seasons. Using multiple regression analysis, independent variables: growth stage, cropping system, districts and altitude were shown to have significant influence on the observed PSI (P<0.05) with R2 = 96.2%. The highest severity (PSI=59.7%) was observed in Kabare district, and the lowest in Uvira district (PSI=39.5%). Screening of a set of 37 released common bean varieties in DRC using virulent Andean and Mesoamerican isolates identified four resistant bean varieties; ARA 4, COD MLV 059, MLV 224/94B, LSA 144 and Mexico 54. Some of these varieties possess useful traits, in addition to acceptable seed market class, and are hence recommended as suitable parents for ALS resistant variety development and promotion in ALS prone environments