Field and laboratory experiments were carried out on the island of Oahu, HI, to compare the susceptibility of the two most commonly grown banana (Musa sp.) cultivars in the state ('Dwarf Brazilian' or Santa Catarina [locally known as dwarf apple] and 'Williams') to the aphid-borne Banana bunchy top virus (genus Babuvirus, family Nanoviridae, BBTV). Several morphological and physiological features of the two cultivars were monitored to determine whether the banana aphid, Pentalonia nigronervosa Coquerel (Hemiptera: Aphididae), transmits BBTV to both cultivars at a similar rate; and whether after successful inoculation, does each cultivar respond similarly to viral infection. Results from the laboratory experiment showed that a similar percentage of both cultivars were infected with BBTV by aphid vectors (> 90% for both cultivars). However, field results showed a significantly lower percentage of dwarf apple (39%) infected with BBTV compared with Williams (79%). We also found that all physiological and morphological features measured (i.e., plant height, leaf area, canopy, chlorophyll level, and moisture content) for both cultivars were impacted similarly by BBTV. The incubation period, or the time between plant infection and initial appearance of disease symptoms, was similar for both cultivars. Results also showed that BBTV transmission efficiency was lower in the field than in the laboratory, despite that more aphids per plant were used for field than laboratory inoculation tests. The results highlight the potential use of less susceptible cultivars to help manage BBTV and the importance of screening banana varieties in the field to determine their response to vectors and associated diseases.

Embryogenic cell suspensions (ECS) initiated from immature male flowers of banana cultivar 'Dwarf Brazilian' (AAB, Pome subgroup) were transformed using Agrobacterium tumefaciens containing one of four constructs derived from the replicase-associated protein (Rep) gene of the Hawaiian isolate of Banana bunchy top virus (BBTV). Each construct was engineered under control of a double CaMV 35S promoter and the AMV enchancer sequence in the binary plasmid pBI121. Constructs were transferred into A. tumefaciens strain AGL0 and used to transform banana ECS. Plantlets that survived antibiotic selection were acclimated to greenhouse conditions and challenged with viruliferous banana aphids (Pentalonia nigronervosa). Ten adult or late instar aphids were allowed to feed for 2-4 weeks on test plants. All test plants were kept in the greenhouse and monitored for symptom expression for a period of 6 months. Control plants transformed with empty vector pBI121 only were included in all tests. A total of 270 test plants and 63 control plants were screened for BBTV resistance using this approach. One of 32 test plants transformed with the M1 (mutant Rep gene) construct, 5 of 74 test plants transformed with the AS1 (antisense Rep gene) construct, 5 of 38 test plants transformed with the PR1 (partial Rep gene) construct, and 10 of 126 test plants transformed with the R/PR1 (full-length Rep gene fused to antisepses partial Rep gene) construct were found to be resistant to BBTV challenge and showed no bunchy top symptoms. All of the control plants became infected with BBTV under these experimental conditions. Plants that survived BBTV challenge were analysed by quantitative PCR (per) and Southern hybridisations to determine the number of transgenes that were present in their genomes. Results from these analyses indicated that the resistant plants contained from 2 to more than 9 copies of the NPTII (kanamycin resistance) transgene carried on the pBI121 plasmid.

Citrus canker caused by Xanthomonas citri subsp. citri (syn. X. axonopodis pv. citri) was first reported in South Texas during the early 1900s, prompting quarantine and eradication programs by the federal government. Its last reported incidence in Texas was from two trees from Corpus Christi in 1943. In May 2016, USDA Animal and Plant Health Inspection Service-Plant Protection and Quarantine (PPQ) confirmed the presence of the Asiatic A strain, which is by far the most widespread and severe form infecting most citrus varieties, on two sour orange trees in a park in Houston. Subsequently, infected trees were detected in a nursery in Richmond (Fort Bend Co.) in August 2016 and in dooryard trees in Pearland (Brazoria Co.) in 2018. PPQ and Texas Department of Agriculture collected a combined 1,949 positive A strain samples from Harris, Fort Bend, and Brazoria Counties during May 2016 to January 2021. These findings resulted in seven active citrus canker quarantine zones being established in the Upper Golf Coast area. The Texas Department of Agriculture is removing positive trees, and surveys are continuing.

The behavior of 10 chironja clones, studied at the Isabela, Corozal and Adjuntas Substations, demonstrated that graftage of chironja on sour orange rootstock is incompatible as determined by the scion to rootstock ratio. This incompatibility increased with tree age and was greatest in Adjuntas, intermediate in Corozal, and least in lsabela. The Adjuntas trees had significantly thinner trunk (either rootstock or scion) diameter, and smaller canopy volume than those of Isabela and Corozal. This probably accounted for the smaller size of fruits and the lower fruit production in Adjuntas as compared to those of Isabela and Corozal. The Isabela trees had significantly greater trunk (rootstock and scion) diameter and smaller scion/rootstock ratio and canopy volume than those of Corozal. The weight and number of fruits per tree increased with age from 1970-1972, while the weight per fruit was reduced at the same time. The chironja clone 2-4 produced significantly the highest crop and the heaviest fruits; therefore, its multiplication should be encouraged.