Common Bean Reaction to Fusarium oxysporum f. sp. Phaseoli, the Cause of Severe Vascular Wilt in Central Africa

During Ihe Seplember- December seasOIl of 1990. severe symptoms of Fusarium wil t were for the first time observed on a popular climbing bean (Plwseo/us lʹldgaris L.) cultiva,- G 2333. inlroduced wilhin Ihe previous 5 years . Seventy-three bean genotypes were scrccned for resistance to the disease. using artilkial inoculation. The enect of inoculum density all the reaction of fOllr selected genotypes was also investigaLcd. Of the 29 climbing bean genOlYpes eval uated. 19 were resista nt. includ ing II of Ihe 15 pre-release or released cuiti vars. Of Ihe 44 bush bean eulti vHrs evaluated. 28 were resis ta nt. five were inlermediale and II were susceptible. All susceplible cui· tivars showed vascular discoloration. In both sllscepti ble and resi slanl genolypes. lhe fungus spread aimosl equa lly from the en try points in inoculated roots to thc base of the plants. but colonization and vertical spread wi thin the vascular system were marked ly less in rcsislHnt than ill susccplible cul li va rs. AI20 and 30 cm above soil level, the fungus was on ly recovered from susceptible culti vars. Increasing inoculum density from 10:! to 107 conidia /ml d id nOI a!Tectlhe resislance of eull ivars R WR 950 and G 685 but, in Ihe suscepli ble culli vars G 2333 and M LB· 48·89 A. il resu lted in early appeara nce. high incidence and severity of the disease.