Choy Sum Research Articles

Prospects for biological control of cutleaf mignonette, Reseda lutea (Resedaceae), by Baris picicornis and Bruchela spp. in Australia

In South Australia, Reseda lutea is abundant, invading pastures and crops on calcareous soils while in its native Mediterranean range it is uncommon in occurrence and is not reported as a weed of cultivated crops. Its invasive behaviour in South Australia may be attributed to vegetative growth of root fragments spread by cultivation, while propagation by seed is of minor importance. Surveys in Spain, Portugal, Morocco, France, Turkey and Israel indicated that agronomic differences, particularly depth of cultivation and seeding rates of cereals may explain why it is not a crop weed in these countries. Another difference is that plants in the region of origin have an associated fauna not present in Australia. These potential biological control agents include a root-boring weevil, Baris picicornis, flower- and seed-feeding urodontids, Bruchela suturalis and B. rufipes, and a leaf spot pathogen,Cercospora resedae. Baris picicornis was introduced from France and Turkey, under quarantine, to Australia but laboratory specificity-testing demonstrated that it could complete its life cycle on 2 commercially grown cultivars of Brassica rapa (choy sum and Chinese cabbage). Because of this, it is not proposed to release B. picicornis in Australia at present. Bruchela suturalis was also introduced into Australian quarantine from France but attempts to change its annual life cycle to Southern Hemisphere seasons were not successful, and a culture could not be established. Both Baris picicornis and Bruchela spp. remain promising agents, and further work on their introduction is justified by their potential for biological control of R. lutea.

ENHANCEMENT OF SENESCENCE IN NON-CLIMACTERIC FRUIT AND VEGETABLES BY LOW ETHYLENE LEVELS

When the non-climacteric fruit and vegetables, strawberries, oranges, lettuce, beans, Chinese cabbage, bak choi, choi sum and gai lan were held at ambient temperature (20°C) and low temperature (0°-2.5°C) and ventilated with air containing ethylene over the range 10 to 0.005 μL/L, the storage life of all produce was found to be linearly extended with a logarithmic reduction in ethylene concentration across the whole concentration range. The ethylene level found to accumulate around produce in the markets was in the range 0.06-1.45 μL/L suggesting that premature ageing occurs in all non-climacteric produce during normal marketing. There appears to be no benign level of ethylene so that any reduction of ethylene concentration should help in maintaining quality of all non-climacteric fruit and vegetables.

Determination of carotenoids in Chinese vegetables

Seven leafy Chinese vegetables, gau choi ( Allium tuberosum), een choi ( Amaranthus tricolor), baak choi ( Brassica chinensis), choi sum ( Brassica parachinensis), wong baak ( Brassica pekinensis), ong choi ( Ipomoea aquatica) and sai yeung choi ( Rorippa nasturtium aquaticum) were analysed for carotenoids by reversed-phase HPLC and gradient elution. Sixteen carotenoids were identified as being present at levels of more than 2% of total carotenoids. For all leafy vegetables, lutein was the major carotenoid with β-carotene present at substantial levels. Violaxanthin, neoxanthin, antheraxanthin and mutatoxanthin were also important contributors in specific produce.

548 PB 096 EFFECT OF METHANOL ON BIOMASS ACCUMULATION AND PHOTOSYNTHETIC EFFICIENCY OF VEGETABLE CROPS IN HAWAII

Methanol sprays reportedly increased yields of several crops in Arizona by 50 to 100 percent (Nonomura and Benson PNAS 89:9794(1992). Reports from other parts of the country have shown conflicting results with regards to the effect of methanol sprays on yields of horticultural crops. Several greenhouse and growth chamber (controlled temperature. day length, and photosynthetic photon flux) experiments were conducted to evaluate the effect of methanol sprays on the growth and productivity of several vegetable crops in Hawaii. Treatment spray solutions consisted of 20-25% methanol, 0.5% low biuret urea. 0.001% chelated iron, and 0.02% surfactant. Control sprays only contained urea, chelated iron, and surfactant. Each experiment consisted of at least 5 weekly methanol sprays. Flowering cabbage, Brassica campestris var. parachinensis, had greater biomass production when sprayed with methanol in the late summer months. Similar results were obtained with choi sum in a 2 by 2 factorial experiment with methanol and water stress treatments. However, choi sum did not respond to methanol treatments in follow-up greenhouse trials. perhaps attributable to the shorter and Overcast days experienced in the fall and winter. Okra, chili pepper, and eggplant showed no response to methanol sprays. Okra showed a trend toward increase yields in response to methanol sprays, but differences were not significant. Follow-up studies in the greenhouse and in the field, which include evaluation of photosynthetic efficiency through chlorophyll fluorescence determinations will be presented.