3rd December 2009: This Entry is Generate to Answer the Issue Raised by CMU'sofficer Blog
Saya pertama sekali ingin mohon maaf kerana baru berkesempatan menjawab isu yang diketengahkan. Gambar yang ditampilkan dalam blog ini agak berbeza dengan gambar yang dipost oleh d' scientist dalam blog CMU. Kejadian ini juga tidak berlaku di Australia sama sekali tetapi di negara kawan kita yang satu lagi bernaung, Cik Mega Arjuna i.e. California, US.
Saya sebenarnya selama ini bertapa kerana Chapter 2 thesis. Kebetulan sesudah menyiapkan draft pertama..Hooorrraaayyyy! saya excidently menemui sindrom penyakit yang dikenali sebagai "Grapevine Trunk Diseases" sebagaimana yang diminta penjelasan oleh CMU. Maaf gambar ini tidak seseksi gambar kalian tapi infonya sangat berguna. Kejadian excidently ini berlaku kerana rupa2nya physiology dan biochemistry di sebalik kejadian ini ada kena mengena dengan topik yang sedang saya bangunkan untuk projek PhD saya iaitu wounding in woody plant spp.
Berikut penjelasan yang sempat saya petik:-
Symptoms of these diseases include dead spurs, arms, and cordons and eventual vine death due to canker formation in the vascular tissue. In Eutypa dieback, deformed leaves and shoots occur as the pathogen invades spur positions. As cankers develop, yield reductions occur due to the loss of productive wood. The impact of grapevine wood diseases can be significant in older vineyards, and usually becomes more severe as vineyards become older.
In this regard, Botryosphaeria species have also been recovered from cankers, and were determined to be the main cause of canker diseases in some California vineyards. Recent research has also indicated the occurrence of several new fungal trunk disease pathogens of grapevine belonging to the family Diatrypaceae (the same family as Eutypa). These include Eutypa leptoplaca, Cryptovalsa ampelina, Diatrype species, and Diatrypella species.
Eutypa lata spreads to new pruning wounds by wind-driven and water-splashed ascospores released during rain events. Ascospores develop inside perithecia (fungal fruiting bodies) that form when the fungus enters its sexual stage. The sexual stage develops on dead wood, where masses of perithecia are produced in a black substrate referred to as stroma. The sexual stage develops in regions that receive over 16 inches of rain. It is common to find stroma and perithecia on old grapevines and other types of wood in the North Coast and Delta production areas.
Ascospores infect grapevines through fresh pruning wounds during the dormant season. They germinate, invade xylem vessels, weaken the plant by producing toxins and cause wood decay by excreting cell wall degrading enzymes.Eutypa lata also produces asexual spores called conidia. These are formed inside pycnidia (another type of fruiting body) that develop on wood, but these conidial spores do not play a role in disease epidemiology.
In California, ascospore discharge of E. lata occurs from the first rain of the early fall until the last rains of the spring. Ascospore discharge decreases significantly in late February and remains low to nil by early March. However, ascospore release may occur during rains in March and April if they are preceded by several weeks of no rain and sunny, warm weather. Such releases may occur because perithecia are able to recover in productivity during the dry period, or because spores that would have been released in the winter months are released in the spring simply because they were not released in the winter. This scenario more often occurs in years when there is little rainfall during the winter months. Ascospore release from individual perithecia may occur continuously for approximately 24 hours during periods of rainfall, starting a few hours after the onset of a rain.
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