Resistance levels of Arabica coffee cultivars to bacterial-halo-blight under field conditions and planting spacings within the rows

Abstract

Bacterial-halo-blight (BHB) is an important coffee disease caused by the Pseudomonas syringae pv. garcae. To date, there are few studies reporting resistance to BHB in adult plants of Arabica coffee cultivars under field conditions. The aim of this study was to assess the levels of resistance to BHB in Arabica coffee cultivars under field conditions and different planting spacings within the rows (SWR). The field trial was assessed for BHB severity in natural infection condition by using a grade scale, ranging from 1 to 5 in Londrina (Paraná state, Brazil) in December 2016 (36 months after planting). The experiment was planted at the 2.50m spacing inter-row, using randomized blocks design in a 4 x 15 factorial scheme with three replications and five plants per plot. The factors consisted of four SWR (0.40m, 0.50m, 0.60m and 0.70m) and 15 Arabica coffee cultivars. The resistance levels were based on the mean BHB severity grades, where the cultivars were classified as highly resistant (HR), resistant (R), moderately resistant (MR), slightly resistant (SR) and susceptible (S). Adult plants of IPR 102 and IPR 106 were HR and MR to BHB, respectively, under natural field conditions. IAPAR 59, IPR 103, IPR 104, IPR 107 and IPR 108 showed a lower level of resistance than the cultivars IPR 102 and IPR 106. Some HdT-derived cultivars such as IPR 97, IPR 98, IPR 99 and Tupi IAC 1669-33, besides cultivars IPR 100, IPR 101 and IPR 105, derived from IAC 1110-8 were susceptible. In the two SWR more densely, the BHB severity was higher, and some cultivars behaved as more susceptible in these spacings.