EFFECT OF SANITARY LEAF PRUNING ON MARGINAL NECROSIS INCIDENCE AND CORMEL PRODUCTION OF COCOYAM (Xanthosoma spp. Schott). DARIEN, PANAMA. 1996-1997.

Abstract

In 1996, a study was realized at IDIAP's experimental field in Santa Fe, Darien Province, Republic of Panama. The research objectives were to evaluate the effect of leaf pruning frequency on sanitary condition and cormel production of cocoyam plants (Xanthosoma spp.) growing in a "Marginal Necrosis" highly infested plot. Traditional cocoyam cultivar "San Andres", susceptible to bacterial necrosis of leaves, caused by Xanthomonas campestris, was planted. Five leaf pruning frequencies (120, 160, 210, 260, and 310 days after planting) were compared against a control treatment without leaf pruning. A Randomized Complete Block design with three replicates was used to distribute treatments. The experimental plot consisted of four rows planted 1 m apart and single cormels sowed at a density of 0.75 m within the rows, equivalent to a planting density of 13,330 plants per hectare. Harvest was realized in late April 1997. Experimental variables were: 1) number of plants killed by Marginal Necrosis disease (%) and 2) total cormel production (t/ha). The ANOVA of experimental data revealed highly significant differences (p<0.001) among treatments (pruning frequencies) in relation to the percentage of cocoyam plants killed by the bacterial disease and the production of cormels. When five sanitary pruning were made, the lowest percentage of killed plants occurred (6.25 %) and the highest cormel production (equivalent to 16.62 metric tons/hectare) was obtained. The bacterial disease killed 56.24% of plants in control plots without sanitary pruning and a poor yield of 3.97 metric tons of cormels per hectare was produced. Correlation coefficients were highly significant for both experimental variables. Percentaje of killed plants was negatively correlated to frequency of sanitary pruning following the linear equation were Y = 56.0366 – 10.87 X. Cormel production was positively correlated to the frecuency of sanitary pruning through the equation T = 3.7190 + 2.7177 X. The partial budgetary analysis indicates that highest revenue (3853 %) was obtained when cocoyam planats received four sanitary prunings.