ISHS Acta Horticulturae 736: III International Date Palm Conference
STUDY ON POSSIBLE INFLUENCE OF PATHOGENIC FUNGI ON DATE BUNCH FADING DISORDER IN IRAN |
| Authors: | F. Karampour, H. Pejman |
| Keywords: | date palm, fruit wilt, toxigenic fungi, environmental stresses |
| Abstract:
Date palm (Phoenix dactylifera L.) is one of the most important commercial fruit trees growing in about 220,000 hectares of Iran, especially in six southern provinces. In accordance with recent investigations, there are more than 400 cultivars in date palm plantations of Iran (Karampour, 2002; Mirzaei et al., 2001). Date bunch fading disorder (DBF) is the most harmful phenomenon that damages both the quality and quantity of date yield. During the last 5 years this disorder has caused wilting and drying of bunches and finally severe defoliation of date fruits in southern Iran, especially on commercial cultivars in khelal-rutab stages. This investigation was carried out during 2002–2004, starting with the collection of more than 150 samples of vegetative and generative tissues of affected trees from Hormozgan and from several areas of south Kerman Province. Samples were collected, cut into 3–5 mm pieces, surface-sterilized in 1% hypochlorite for 2–3 minutes, then placed on potato dextrose agar (PDA) containing 1 ml/L lactic acid (25% concentration) and incubated at 26 ±1ºC for one week. The fungi Aspergillus niger, A. flavus, A. sp., Alternaria sp., Trichoderma sp., Penicillium spp. Thielaviopsis paradoxa, Fusarium sp. and Rhizoctonia sp. were isolated. All fungi obtained from infected generative tissues such as pedicels, strands and peduncles exclusively, were purified and identified as associated fungi based on morphological and growth characters. The asexual stage of Ceratocystis paradoxa was isolated from more than 50% of infected vegetative samples. This fungus was identified by the production of two types of spores; the dark cylindrical microconidia which formed endogenously in uniseriate chains, and ovate macroconidia measuring 11–16 × 8–15 µm. Pathogenicity tests were carried out under laboratory conditions (T: 35 ±5°C, Rh: 25 ±5%) on the cut bunches (in vitro) and under natural conditions in the orchard in a RCB statistical design on susceptible cultivar ‘Mordaseng’, during August – September of two years. Among nine species of associated fungi, the thermophillic fungus Thielaviopsis paradoxa produced symptoms similar to DBF disorder, both in vitro and in vivo. Also two species of Aspergillus spp. produced necrotic longitudinal lesions similar to DBF disorder on the cut peduncles under in vitro conditions only. It is likely that with date palm, T. paradoxa is an opportunistic secondary pathogen attacking stressed trees (in this case, the affected trees were growing under conditions of severe drought, hot winds and salinity. T. paradoxa which also causes terminal bud rot, black scorch and bending head diseases on date palms in southern Iran (Karampour et al., 2002), is a widespread fungus and its pathogenicity to date palm is well documented, especially in areas where drought and salinity are prevailing (Abbas et al., 2003; Carpenter et al., 1966; Elmer et al., 1968; Karampour et al., 2002; Ploetz et al., 2003). Date bunch fading disorder (DBF) has not been observed and reported in the world until now. This is the first report of DBF disorder from Iran and the world. | |
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