Effects of flooding on grafted annona plants of different scion/rootstock combinations

Annona atemoya Hort cv. African Pride (AP) is highly valued due to its high quality and unique flavor, but highly susceptible to water-logging. Prevalence of root diseases in saturated soils is one of the main problems in production, which restricts the development of AP in south China, where flooding frequently occurs in rainy seasons. However, some annona species, e.g. A. montana, A. glabra and A. muricata, are relatively tolerant to continuous flooding and periodic water-logging conditions, but of limited commercial value. Yet, the potential may exist to increase flood tolerance of commercial annona varieties by the use of flood tolerant rootstocks. An experiment was conducted with the aim to study the effects of continuous or periodical soil flooding on tree performances of four different annona scion/rootstock combinations: AP/AR/G (scion/interstock/rootstock), AR/G (scion/rootstock), AP/AR/M and AR/M, where AP stands for Annona atemoya Hort cv. African Pride, AR for the hybrid of “AP” atemoya × A. reticulata, used as an interstock, G for pond apple (A. glabra), and M for mountain soursop (A. montana). Plant growth, leaf net photosynthetic rates and chlorophyll fluorescence parameters were measured regularly after flooding treatments were applied. Flooding treatments reduced shoot extension, leaf production, net photosynthetic rates and maximum quantum efficiency of photosystem II (Fv/Fm) in plants of AP/AR/M and AR/M, which displayed wilting within 2 weeks of flooding, with a higher wilting percentage in AP/AR/M than in AR/M. The wilted plants shed all leaves but remained alive and sprouted new but weak shoots after 16 weeks of flooding. Long term flooding did not suppress but enhanced photosynthesis as well as tree growth in AP/AR/G and AR/G, with vigorous growth of adventitious roots. Thus, we suggest the use A. glabra instead of A. montana as a rootstock and AR as an interstock to increase flood tolerance of commercial annona varieties.

Stress Effects of Chlorate on Longan(Dimocarpus longan Lour.)Trees: Changes in Nitrogen and Carbon Nutrition

Three-year-old potted longan(Dimocarpus longan Lour.cv.Shixia)trees were treated with potassium chlorate and effects on nitrogen and carbon nutrition were examined.The results showed that potassium chlorate at 10 and 20 g per pot failed to induce flower but suppressed shoot growth and caused leaf chlorosis and drop.The treatment significantly inhibited nitrate reductase but increased nitrogen concentration in the leaves and buds.Concentration of soluble amino acids in the leaves of treated trees increased within 14 days and then declined to the control level,while it increased constantly in buds.In both organs,the amino acid increase was an all-round one,with all the tested 21 amino acids increased.However,soluble proteins in the leaves were slightly increased by chlorate,indicating that de novo synthesis of amino acids was activated.Chlorate reduced photosynthetic rate and stomatal conductance but slightly increased CO2 concentration in the mesophyll,suggesting that chlorate treatment damaged photosynthetic apparatus.The damage was reflected by the destruction of thylakoids and grana in the chloroplasts.Chlorate also caused depletion of starch with significant accumulation of soluble sugars in the leaves.Accumulation of sugars and soluble amino acids indicates osmotic adjustment in response to the stress caused by chlorate treatment.