The inflorescences of date palm (Phoenix dactylifera) develop within the crown of the tree, at the base of the leaves, from meristems located as deep as 1 m within the upper part of the trunk (Tomlinson, 1990; Zaid and De Wet, 1999). Each inflorescence is enclosed by a single hard, sealed protective cover, the prophyll (commonly called spathe). The inflorescence is branched with numerous first-order rachilae immerging from the main inflorescence stem, the peduncle (called “fruit stalk” by farmers) (Chao and Krueger, 2007; Dransfield et al., 2008; Tomlinson, 1990). The fruit stalk continues to elongate for several weeks after fertilization (Chao and Krueger, 2007; Dransfield, et al., 2008). Fruit stalk drying and rot in date palm has been observed for decades and was described as early as the 1930s (Bliss, 1937). This phenomenon, previously described as “cross-cut” or “V-cut,” is expressed as cuts in the fruit stalk, which cause the drying and dropping of fruit bunches. These symptoms have been commonly observed in many date-growing regions, particularly in the Sayer and Khadrawi cultivars and occasionally in ‘Dayri’, ‘Maktoom’, and ‘Halawi’ (Bliss, 1937; Brown and Butter, 1936; Carpenter and Elmer, 1978; Stoler, 1977; Zaid et al., 1999). Damage appears intermittently, but, in specific years, can cause up to 25% crop loss (Bliss, 1937). Cross-cuts are most commonly found in relatively slow-growing cultivars with densely arranged leaf bases and the severity of damage increases with the age of the tree (Carpenter and Elmer, 1978).
Recently, severe damage to Medjool cultivar resulting from bunch drop has been observed in Israel. In some areas, up to eight bunches, out of a total of 25 to 30, were lost from each tree, which may reach up to 30% yield loss. Both fractures and rot occurred during fruit stalk development deep within the crown.
Three major causal agents have been suggested as possible factors in this phenomenon: 1) mechanical cracks of unclear origin occurring in the soft tissues of the fast-growing fruit bunch (Bliss, 1937); 2) pathogen infection [necrosis has often been observed at the cuts, suggesting the involvement of fungal pathogens in the process (Bliss, 1937)]. However, it is not clear whether these pathogens play a primary or secondary role in this phenomenon; and 3) larvae of the greater date moth (Arenipses sabella Hampson) overwintering within the bases of the leaves within the date crown and feeding on developing fruit stalks (Okko, 2004).
Bliss (1937) suggested that Fusarium sp. may be involved in the process. Recently, Fusarium proliferatum has been isolated from roots and leaves of declining date palm (Abdalla et al., 2000) and other palm species (Armengo et al., 2005), but these studies have not mentioned any role for this pathogen in fruit bunch drop.
The aims of this study were to characterize the phenomenon of bunch drop in ‘Medjool’ date palm and elucidate the role of the previously mentioned factors in this phenomenon.
Abdalla, M.Y., Al-Rokibah, A., Moretti, A. & Mulè, G. 2000 Pathogenicity of toxigenic Fusarium proliferatum from date palm in Saudi Arabia Plant Dis. 84 321 324
Armengo, J., Moretti, A., Perrone, G., Vicent, A., Bengoechea, J.A. & Garcia-Jimenez, J. 2005 Identification, incidence and characterization of Fusarium proliferatum on ornamental palms in Spain Eur. J. Plant Pathol. 112 123 131
Carpenter, J.B. & Elmer, H.S. 1978 Pest and diseases of the date palm U.S. Department of Agriculture Handbook No. 527 Washington, DC 42
Chao, C.T. & Krueger, R.R. 2007 The date palm (Phoenix dactylifera L.): Overview of biology, uses, and cultivation HortScience 42 1077 1082
Dransfield, J., Uhl, N.W., Asmussen, C.B., Baker, W.J., Harley, M.M. & Lewis, C.E. 2008 Genera palmarum: The evolution and classification of palms Kew Publishing Kew, UK
Liebenberg, P.J. & Zaid, A. 1999 Date palm irrigation 130 143 Zaid A. Date palm cultivation Plant Production and Protection Paper No. 156 FAO, Rome, Italy
Mulè, G., Susca, A., Stea, G. & Moretti, A. 2004 A species-specific PCR assay based on the calmodulin partial gene for identification of Fusarium verticillioides, F. proliferatum and F. subglutinans Eur. J. Plant Pathol. 110 495 502
Nash, S.N. & Snyder, W.C. 1962 Quantitative estimations by plate counts of propagules of the bean rot fusarium in field soils Phytopathology 73 458 462
Sokal, R.R. & Rohlf, F. 1981 Biometry: The principles and practice of statistics in biological research 2nd Ed W.H. Freeman San Francisco, CA
Tripler, E., Ben-Gal, A. & Shani, U. 2007 Consequence of salinity and excess boron on growth, evapotranspiration and ion uptake in date palm (Phoenix dactylifera L., cv. Medjool) Plant Soil 297 147 155
Zaid, A. & De Wet, P.F. 1999 Botanical and systematic description of the date palm 29 44 Zaid A. Date palm cultivation Plant Production and Protection Paper No. 156 FAO, Rome, Italy
Zaid, A., De Wet, P.F., Djerbi, M. & Oihabi, A. 1999 Diseases and pests of date palm 223 287 Zaid A. Date palm cultivation Plant Production and Protection Paper No. 156 FAO, Rome, Italy