Susceptibility of low-chill blueberry cultivars to Mediterranean fruit fly, oriental fruit fly, and melon fly (Diptera: Tephritidae).

No-choice tests were conducted to determine whether fruit of southern highbush blueberry, Vaccinium corymbosum L., hybrids are hosts for three invasive tephritid fruit flies in Hawaii. Fruit of various blueberry cultivars was exposed to gravid female flies of Bactrocera dorsalis Hendel (oriental fruit fly), Ceratitis capitata (Wiedemann) (Mediterranean fruit fly), or Bactrocera cucurbitae Coquillet (melon fly) in screen cages outdoors for 6 h and then held on sand in the laboratory for 2 wk for pupal development and adult emergence. Each of the 15 blueberry cultivars tested were infested by oriental fruit fly and Mediterranean fruit fly, confirming that these fruit flies will oviposit on blueberry fruit and that blueberry is a suitable host for fly development. However, there was significant cultivar variation in susceptibility to fruit fly infestation. For oriental fruit fly, 'Sapphire' fruit produced an average of 1.42 puparia per g, twice as high as that of the next most susceptible cultivar 'Emerald' (0.70 puparia per g). 'Legacy', 'Biloxi', and 'Spring High' were least susceptible to infestation, producing only 0.20-0.25 oriental fruit fly puparia per g of fruit. For Mediterranean fruit fly, 'Blue Crisp' produced 0.50 puparia per g of fruit, whereas 'Sharpblue' produced only 0.03 puparia per g of fruit. Blueberry was a marginal host for melon fly. This information will aid in development of pest management recommendations for blueberry cultivars as planting of low-chill cultivars expands to areas with subtropical and tropical fruit flies. Planting of fruit fly resistant cultivars may result in lower infestation levels and less crop loss.

Host status of Vaccinium reticulatum (Ericaceae) to invasive tephritid fruit flies in Hawaii.

Ohelo (Vaccicinium reticulatum Small) (Ericaceae) is a native Hawaiian plant that has commercial potential in Hawaii as a nursery crop to be transplanted for berry production or for sale as a potted ornamental. No-choice infestation studies were conducted to determine whether ohelo fruit are hosts for four invasive tephritid fruit fly species. Ohelo berries were exposed to gravid female flies ofBactrocera dorsalis Hendel (oriental fruit fly), Ceratitis capitata (Wiedemann) (Mediterranean fruit fly), Bactrocera cucurbitae Coquillet (melon fly),or Bactrocera latifrons (Hendel) in screen cages outdoors for 24 h and then held on sand in the laboratory for 2 wk for pupal development and adult emergence. Only B. dorsalis successfully attacked and developed in ohelo berries. In total, 1570 berries produced 10 puparia, all of which emerged as adults, for a fruit infestation rate of 0.0064% and an average of 0.0053 puparia per gram of fruit. By comparison, papaya fruit used as controls produced an average of 1.44 B. dorsalis puparia per g of fruit. Ohelo berry is a marginal host for B. dorsalis and apparently a nonhost for C. capitata, B. cucurbitae, and B. latifrons. Commercial plantings of ohelo will rarely be attacked by fruit flies in Hawaii.

Host status of blueberry to invasive tephritid fruit flies in Hawaii.

Forced infestation studies were conducted to determine whether northern or southern highbush blueberries, Vaccinium corymbosum L., are hosts for the invasive tephritid fruit flies in Hawaii. Fruit were exposed to gravid female flies of Bactrocera dorsalis Hendel (oriental fruit fly), Ceratitis capitata (Wiedemann) (Mediterranean fruit fly), or Bactrocera cucurbitae Coquillet (melon fly) in screen cages outdoors for 6 h and then held on sand in the laboratory for 2 wk for pupal and adult emergence. The number of puparia, number of puparia per gram, and percentage of adult emergence on 'Bluecrop' blueberry were significantly higher for B. dorsalis and C. capitata than B. cucurbitae; B. dorsalis, C. capitata, and B. cucurbitae produced an average of 1.06, 0.60, and 0.09 pupae per g fruit and had 5.8, 54.1, and 12.7% adult emergence, respectively. 'Berkeley' blueberries produced an average of only 0.06, 0.02, and 0.0 pupae per g fruit for B. dorsalis, C. capitata, and B. cucurbitae, respectively. Similarly, six blueberry cultivars were harvested weekly for 10 wk, exposed to Bactrocera latifrons (Hendel) in cages, and held for pupal and adult emergence on either sand or artificial diet. In total, 2,677 blueberries were exposed to 2681 B. latifons and held on sand, and no pupariation or adult emergence was observed. Small numbers of B. latifrons puparia and adults emerged from the artificial diet treatment in all cultivars. Results from rearing on sand and diet indicate that blueberry is an acceptable oviposition host for B. latifrons but not an adequate developmental host. These data suggest blueberry is potentially a good host for B. dorsalis and C. capitata, and an adequate host for Bactrocera cucurbitae, but that there may be significant variation in resistance among cultivars. Blueberry seems to be a nonhost for B. latifrons.

Identification and Characterization of Pestalotiopsis spp. Causing Scab Disease of Guava, Psidium guajava, in Hawaii.

Guava is one of the most widely grown plants in the tropics; however, it is affected by many fruit rot diseases. Fruit diseases decrease the marketability of fresh fruit and fruit for processing. A survey of scab disease was conducted at the USDA/ARS Tropical Plant Genetic Resource Management Unit in Hilo, HI, where more than 50 accessions of guava are grown. Symptoms observed were gray/light brown lesions surrounded by dark brown borders on leaves and brown, raised, corky, necrotic lesions on the exocarp of fruit which progressed as the fruits matured. Seventeen isolates from infected fruit, six isolates from lesions on leaves, and nine isolates from additional crops surrounding the guava trees were collected. The main fungi consistently isolated from symptomatic leaves and fruit were Pestalotiopsis spp. Morphology, colony characteristics, and pathogenicity of the isolates were examined and potential sources of host resistance were identified for germplasm characterization studies. Molecular methods were used to identify four Pestalotiopsis taxa (P. clavispora, P. microspora, P. sp. GJ-1, and P. disseminata) on guava in Hawaii. To our knowledge, this is the first report of traditional and molecular methods of identification and characterization being used for fungal pathogens of guava in Hawaii.

Isolation and Characterization of Burkholderia gladioli from Orchids in Hawaii.

Bacterial diseases of orchids continue to be serious problems. Bacterial strains were isolated from orchid plants exhibiting disease symptoms in Hawaii. Small to large leaf spots with or without water-soaking or soft rots were observed on various orchid genera, including Dendrobium, Oncidium, and Miltonia spp. and hybrids. Bacteria isolated and cultured from the lesions were tentatively identified using analytical profile index (API) strips and standard physiological and biochemical tests, and confirmed by species-specific polymerase chain reaction and sequencing of the 16S rRNA gene. The variation in pathogenic, morphological, cultural, and molecular characteristics of the orchid isolates also was evaluated. In our studies, a gramnegative, aerobic, rod-shaped bacterium that produced pale yellow, opaque, round colonies with entire margins on nutrient broth yeast extract agar (NBY) was isolated consistently from diseased orchid plants. On yeast dextrose calcium carbonate agar, the isolates produced brownishyellow, nonmucoid colonies, with the majority of the strains secreting a diffusible yellow or tan pigment into the media. The bacterium was identified as Burkholderia gladioli. Molecular analysis indicated very little diversity in the 16S rDNA gene. Testing B. gladioli isolates using media containing copper or streptomycin indicated varying levels of resistance (copper resistant = Cur; streptomycin resistant, Smr), with approximately 75% of the strains resistant to copper and 94% of the strains resistant to streptomycin. The minimum inhibitory concentration (MIC) of cupric sulfate among Cur strains ranged from 50 to 1,000 µg/ml and the MIC of streptomycin was 50 to 100 µg/ml for all Smr B. gladioli strains tested. Field and laboratory data suggest the frequent use of these chemicals in nurseries may have inadvertently resulted in the development of copper and streptomycin resistance in B. gladioli from orchids.

A primitive Y chromosome in papaya marks incipient sex chromosome evolution.

Many diverse systems for sex determination have evolved in plants and animals. One involves physically distinct (heteromorphic) sex chromosomes (X and Y, or Z and W) that are homozygous in one sex (usually female) and heterozygous in the other (usually male). Sex chromosome evolution is thought to involve suppression of recombination around the sex determination genes, rendering permanently heterozygous a chromosomal region that may then accumulate deleterious recessive mutations by Muller's ratchet, and fix deleterious mutations by hitchhiking as nearby favourable mutations are selected on the Y chromosome. Over time, these processes may cause the Y chromosome to degenerate and to diverge from the X chromosome over much of its length; for example, only 5% of the human Y chromosome still shows X-Y recombination. Here we show that papaya contains a primitive Y chromosome, with a male-specific region that accounts for only about 10% of the chromosome but has undergone severe recombination suppression and DNA sequence degeneration. This finding provides direct evidence for the origin of sex chromosomes from autosomes.