Influence of Altitudes on Sporangia Size and Aggressiveness of Phytophthoracolocasiae Isolates in Cameroon

A study was carried out in four altitudes in Cameroon to assess the size of the sporangia and the aggressiveness of Phytophthoracolocasiae isolates on taro cultivars. The study was conducted in the West and Littoral regions, which include high, medium and low altitude. Sporangia sizes were measured with the microscope on 50 sporangia collected from each isolate and the cross infectivity of the isolates was assessed on leaf fragments of four cultivars; namely Green Purplish Petiole (GPP), Pink Petiole (PP), “White” Petiole Large Blade (WPLB) and “White” Petiole Small Blade (WPSB). Results showed that sporangia measured 40.2-52.3 x 20.3-24.5 µm with a length into width ratio of 1.9-2.2 and a pedicel of 2- 4.3µm. Sporangia from highland and medium altitude isolate of P. colocasiae were larger than those from lowland. Likewise, sporangia from taro cultivar GPP were larger than those from PP cultivar. In term of pathogenicity, the isolates were more aggressive on their cultivar of origin than the other cultivar and those from the lowland formed larger lesion than those from medium and high altitude. The study indicates that sporangia size and infectivity of P. colocasiae varied with the cultivar of origin of the isolate and the altitude.