Evaluation location: Puerto Rico, United States
Musa spp. synthetic hybrids were obtained as virus-indexed in vitro tissue cultured plantlets or adventitious sword sucker meristems for in vitro induction, either from Bioversity International's Musa International Transit Center at the Catholic University in Leuven, Belgium, or directly from one of several other international Musa breeding programs. Following acclimatization in greenhouses, plants were field established on 20 February 2008 at the USDA-ARS Tropical Agriculture Research Station (TARS) research farm in Isabela, PR (18 28'18.38"N, 67 3'4.25"W; elevation 118 masl). A total of 16 individual treatments, including resistant and susceptible checks, were established in a randomized complete block design (RCBD) experiment with four blocks and six single plant experimental units per block. Treatment blocks were spaced 1.5 m between plants and 3.0 m between rows with two rows of three replicate plants consisting of a treatment. Border rows of 'Grand Nain' were established around each treatment and block to ensure uniform disease pressure. Commercial practices for irrigation, fertilization and insect control were followed throughout during the evaluation. Fungicide applications for disease control were excluded.
Gauhl's modification of Stover's Sigatoka severity scoring system, adapted from, was utilized. The scoring system follows a 0 to 6 scale where, 0 = no symptoms; 1 = 1%; 2 = 2 to 5%; 3 = 5 to 15%; 4 = 16 to 33%; 5 = 34 to 50%; and 6 = > 50% of leaf area affected. Beginning 6 months after field establishment, which corresponded to the first appearance of BLS symptoms, every leaf on individual plants was scored monthly for two full crop cycles (mother and first ratoon). Disease severity was also recorded at flowering and harvest during both production cycles. During both cropping cycles, the following agronomic and bunch characteristics were recorded: length of crop cycle, number of functional leaves at flowering and harvest, plant height and pseudostem diameter at flowering, bunch weight, and number of hands and fruit per bunch. In addition, the weight of third hand fruit as well as the length and diameter for the middle six fruits in the third hand were recorded. Analysis of variance was carried out using the GLM procedure of SAS for Windows Ver. 9.1. After significant F test at *P <0.05, mean separation was performed with the least significant difference test.
***Descriptor data represents combined mother (1st) and ratoon (2nd) cycles.