Genetic diversity, physiology and production of Chinese water chestnut (Eleocharis dulcis (Burm. f.) Trin. ex Henschel)

Chinese water chestnut (Eleocharis dulcis (Burm. f.) Trin. ex Henschel) is a new aquatic vegetable to Australia. Lack of research on this crop greatly limits the understanding of its production performance. Therefore, studies on several aspects of this crop were undertaken to provide a scientific basis for improvement in yield and quality.

Firstly, the genetic relationship of Chinese water chestnuts growing in Australia was assessed by using random amplified polymorphic DNAs (RAPDs). For the genetic

analysis of wild putative E. dulcis, three primers separated the samples from 9 out of 10 sites into two distinct groups: E. dulcis and E. sphacelata. In the genetic analysis of samples from cultivated E. dulcis plants, 96 RAPD markers generated by 14 primers separated the samples from Taiwan (var. Shu-Lin), Hangzhou, China (cv. Da Hong Bao), New South Wales, Australia (unknown variety) and the USA (unknown variety) from the rest of the samples from Australia. The remaining samples were too closely related (0.74-4.4% dissimilarity) to be differentiated.

Secondly, the possibility to extend availability of fresh Chinese water chestnut corms by physiological manipulation (photoperiod control) was evaluated in four

photoperiod experiments. When measured, above -ground growth and dry matter production of the whole plants were not significantly affected by photoperiods (8-24 h). However, corm formation was strongly retarded by long days and promoted by the photoperiod which was shorter than a critical value. Under shorter days, significantly more dry matter was shifted towards corms as well as rhizomes, an

effect that became more pronounced as the period of treatment was lengthened.

Thirdly, Chinese water chestnut production in relation to harvest date and cold storage of 'seed' corms was investigated in two experiments. In the first experiment,

March -planted plants were harvested from July to September. Mature corms from each harvest were subsequently stored at 4°C. In terms of corm formation and

maturation as well as soluble sugar concentration in mature corms, the harvests in August were more favorable. After storage at 4°C for 86 d (harvest on 24 September)

to 159 d (harvest on 15 July), no sign of rot nor flesh deterioration was observed. Loss of fresh weight ranged from 0.46% to 6% with the lower value associated with

the shorter storage duration. Corm germination was also favored by shorter storage period. The highest values for the number of sprouts and stems per viable corm and

the length of the longest stem per viable corm were obtained from the harvests on 29  July (139 d storage), 13 August (130 d storage) and 27 August (116 d storage)

respectively. In the second experiment, corms harvested on different dates over the period July to November were stored at 4°C for four different periods prior to planting. Both harvest date and cold -storage duration exhibited significant influence on soluble solid content (°Brix) with the highest values for the first harvest and no cold storage, although the average °Brix value was low for all treatments. Harvest

date and cold -storage duration also showed significant effects on corm sprouting performance evaluated as the number of sprouts and stems, and the length of the

longest stem per viable corm. Average yield per plant showed little difference across `seed' corm harvest dates with the exception of the last. The fresh weight of individual corms was significantly affected by 'seed' corm harvest date but not by storage duration.

Fourthly, the possibility of Chinese water chestnut in vitro culture was investigated with several different explants and culture media. Among all the explants examined, only young rhizome nodes and tips, dormant buds and corm skin with bud scars (buds removed) responded to in vitro culture by the production of shoots or shoot clusters. Root initiation was readily stimulated in the derived microshoots. The test

tube plantlets were successfully transferred to the screenhouse, and their subsequent performance compared favorably with that of corm -derived plants. 

Lastly, a putative Chinese water chestnut disease, tip yellowing and brown stem lesions, which was observed in the greenhouse and in the field, was studied. As no

corresponding symptoms showed up when healthy plants were inoculated with spores derived from the isolates obtained from affected tissue, a nutritional disorder,

perhaps potassium deficiency, was therefore suggested to have been responsible for the symptoms.