{"id":46944,"date":"2022-08-05T11:27:19","date_gmt":"2022-08-05T11:27:19","guid":{"rendered":"https:\/\/dev.metos.global\/?page_id=46944"},"modified":"2023-06-21T08:02:58","modified_gmt":"2023-06-21T08:02:58","slug":"disease-models-olive","status":"publish","type":"page","link":"https:\/\/metos.global\/en\/disease-models-olive\/","title":{"rendered":"Disease models – olive"},"content":{"rendered":"\t\t
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Olive<\/b> disease models\n<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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The olive (Olea europaea L.<\/em>), grown on over 8 million hectares, is the second most important oil fruit tree crop worldwide after oil palm and its cultivation is traditionally concentrated in the Mediterranean area. The total olive oil production for the 2006\u20132007 season was 2.859,500 tons (International Olive Oil Council (IOOC) data). Southern European countries account for about 74.9% of the world production, with Spain being the main producer (38.7%), followed by Italy (21%) and Greece (12.9%). Other important olive oil producers are Turkey, Tunisia and Syria (17.1%) as well as Jordan, Morocco and Algeria.<\/p>

Peacock spot is also known as Olive scab and leaf spot and is widespread in all the major olive growing regions of the world (Obanor et al. 2005). Symptoms have been found to occur mainly on leaves and appear as dark green to black spots surrounded by a yellow halo similar to the eye spot on peacock\u2019s feathers; hence, the name peacock spot (Graniti 1993; Shabi et al. 1994). Peacock spot is considered to be the most important olive grove disease in Spain (Trapero and Blanco, 2008). Crop losses arise mostly from defoliation of infected trees, poor growth and dieback of defoliated branches and reduced fruit yield (Graniti 1993; Viruega et al. 1997). Heavy defoliation has been reported to cause a delay in ripening and a decrease in oil yield in Italy (Graniti 1993) and New Zealand (MacDonald et al. 2000).<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t

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OLIVE SCAB OR LEAF SPOT \u2013<\/br>Venturia oleaginea<\/em><\/a><\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\n\t\t\t\t\t\t\n\t\t\t\t\t\t\t\t\tRecommended equipment<\/span>\n\t\t\t\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t<\/section>\n\t\t\t\t
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Olive Scab<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Olive scab or leaf spot, caused by the fungus Spilocaea oleagina<\/em>, is widespread in the Mediterranean region. Losses arise mostly from the defoliation of severely infected trees, with consequently reduced yield.<\/p>

Symptoms<\/h3>

Symptoms are mainly confined to leaves and appear as dark brown, circular, zonate spots surrounded by yellow haloes (\u2018peacocks eye\u2019). S. oleagina<\/em> shows a typical subcuticular growth, forming flat colonies within the cutinized layer of the thick epidermal cell wall. This habit has been associated with a defence reaction of the host involving mobilization and breakdown of the phenolic glucoside oleuropin and inhibition of pectolytic enzymes produced by the pathogen. The disease is particularly severe in densely planted groves of susceptible olive cultivars and in nurseries. Infections may occur throughout the year, except during hot and dry summers, when favorable temperatures (opt. 16\u201321\u00b0C) and rain occur. Conidia, formed at the apex of short ampulliform conidiophores, are usually carried by rain droplets, but recent data show that humid air currents and insects also contribute to limited aerial dissemination. Usually, the incubation period is about 2 weeks; however, if the infection is followed by a hot season, it may last several weeks. Spots already formed in spring may stop growing in summer and resume their growth and sporulation in autumn. Chemical control schedules include fungicide (especially copper) treatments during the main infection seasons (spring and autumn).<\/p>

Disease Life Cycle<\/h3>

Heavily infected leaves and fruits on the ground, as well as on those that remained on the tree, are a\u00a0source of inoculum<\/u> for the current season or allow over-wintering of the fungus. The pathogen is known generally to survive unfavorable conditions, e.g. dry, hot weather, in fallen leaves as well as in infected leaves on the tree. The conidia formed in leaves on the tree can survive for several months; although once they have separated from the conidiophores they lose their germination ability in less than a week (Viruega and Trapero 1999). Following a period of\u00a0moist warm weather<\/u>\u00a0new batches of conidia are readily produced on the foliar spots. Viable conidia are also produced in fallen leaves. However, their role as inoculum to produce new infections is considered to be negligible (Trapero and Blanco 2008). This study has shown that the disease generally is\u00a0favoured by cool weather<\/u>; however, the warm and humid weather during the summer of 2009 was also observed to encourage disease occurrence. These observations support those of Viruega and Trapero (1999), who found that in Spain leaf infections can remain latent over summer without causing any leaf drop and are the main source of inoculum for autumn\u2013winter infection. Observations also indicated that\u00a0young leaves<\/u>\u00a0were very susceptible to infection in spring, and that foliage in lower parts of trees was more frequently infected. This is consistent with the pathogen\u2019s requirement for high humidity to develop.\u00a0Germination requires 98% humidity, with temperatures in the range of 0\u201327\u00b0C (Trapero Cassas 1994). In Australia, the disease can be inactive during the hot and dry summers. Germination of the spores is restricted at temperatures above 30\u00b0C. The\u00a0percentage of germinating conidia decreases linearly in proportion to leaf age, being 58% at 2 weeks and 35% at 10 weeks<\/u>. Temperature significantly affects the frequencies of conidium germination on wet leaves from 5\u00b0C to 25\u00b0C. The per cent\u00a0germination increases from 16.1, 23.9, 38.8 to 47.8 and decreases again to 35.5% after 24 h<\/u>. Formation of appressoria occurred 6 h after the first signs of germination. The percentage of germlings with appressoria increases with increasing temperature to a maximum of 43% at 15\u00b0C. No appressoria are formed at 25\u00b0C after 48 h of incubation. Increasing\u00a0wetness duration<\/u>\u00a0causes increasing numbers of conidia to germinate at all temperatures tested (5\u201325\u00b0C). The minimum leaf wetness periods required for germination at 5, 10, 15, 20 and 25\u00b0C were 24, 12, 9, 9 and 12 h, respectively. At 20\u00b0C, a shorter wetness period (6 h) is sufficient if germinating conidia were then placed in 100% RH, but not at 80 or 60%. However,\u00a0no conidia germinate without free water even<\/u>\u00a0after 48 h of incubation at 20\u00b0C and 100% RH. The graphical presentation of the Peacock spot model shows the\u00a0leaf wetness, relative humidity and air temperature<\/u>\u00a0together with the results for\u00a0infection<\/u>\u00a0progress and\u00a0infection severity<\/u>. The graph below indicates an infection starting on December 17th at 19:00 and finishing by 100% on December 18th at 11:00. The infection severity is calculated after a longer moist period and it increases\u00a0in steps to 4<\/u>, which means the\u00a0highest calculated severity<\/u>\u00a0for this infection period.<\/p>

Literature:<\/em><\/p>