海南油棕果腐病的病原鉴定及发病条件的研究

三年来作者对于幼龄結果油棕的果穗和果实腐烂的症状、分布、蔓延为害,其发生条件和栽培管理的关系进行了詳細的調查和观察,并进行了病原分离、培养、田间人工接种和試探性化学保护等試驗。同时对果实离层組織的形成进行了切片检查。 結果指出海南十二个地区的幼龄结实棕园普遍出現的花、果、穗腐与环境条件和栽培管理有密切关系。果腐是果实离体后从蒂部組織开始的。从腐果組織中經常可以分离到細菌、炭疽菌和鐮刀菌。多次田間接种証明这些菌对健康果实和果穗均无致病能力。大田喷药无效。看来,油棕果腐病是由于环境坏、管理差的条件下,未成熟或接近成熟的果实产生离层而与果柄分离,再由外界杂菌腐食脫果而致腐烂。可見,本病是屬于非侵染性的生理病害。

INVESTIGATIONS ON THE CAUSAL ORGANISMS AND DEVELOPMENT OF FRUIT ROT OF OIL PALM (ELAEIS GUINEENSIS)

Fruit rot or bunch rot of oil palm in Hainan Island causes a considerable loss. Investigations show that this disease occurs almost all the year round. In dry seasons it appears as a dry rot and during rainy seasons it turns into a soft rot. Symptoms of dry rot always appear as a bunch of yellow, sometimes brown, colored fruit which are at first moribund, then rot off during the ensuing rain, while those of soft rot are quite inconspicuous at their early stages of development. The only way to detect its presence is to hold each fruit between the finger and thumb and shake it gently. Sound fruit always remain rigid on the bunch and diseased ones can be easily taken out of their enfolding brackets. In a more advanced stage, the detached ends turn brown or brownish black, often carrying a light growth of fungus mycelium. In severe cases the brown ends turn into a water soaked appearance, emitting a fouly odor. Rot usually commences at the top fruit of a bunch, extending downward and inward, finally engulfing the whole bunch. During our three years of systematic investigation we have noticed that 1. Plants which were well fertilized and fruit bunches hand pollinated yield only half as much rotted fruit as those of unconcerned ones. 2. Fruit rot on well managed level land is decidedly less than on slopes. 3. Plants growing on soils with a fairly high underground water level (about 1 1/2 to 2 meters from ground level) do not yield as much rotted fruit as those on high land. 4. This disease neither spreads from bunch to bunch nor attacks the trunk or the leaf base of the plant. 5. A green rind variety suffers less fruit rot than the purple rind variety. Isolations from points of detached ends of fruit frequently yield species of Fusarium. Gloeosporium and various kinds of bacteria, and inoculations by various methods to healthy fruit have never induced rot of any kind. During the process of isolation, with the help of free hand sectioning of severed ends under the microscope, we noticed the fact that some detachable fruit during their early stages do not harbour any organisms at all. In order to clarify the case, we carefully removed the fruit with their peduncles attached from bunches showing early signs of shedding. These were cut longitudinally along their medulla into sizes good enough for both paraffin embedding and free hand sectioning. Cut sections reveal the fact that some inmature fruits produce abscission layers much earlier than healthy mature fruit. This would indicate that fruit bunches of oil palms under certain adverse conditions tend to shed their fruit. Since each small fruit is held within three spiny brackets, the upward growing fruit can not easily drop out of the socket; hence, it has to rot in situ. Relating all the observations mentioned above, we believe that this disease is of a physiological nature.