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The weather and climate have strong influence on Forest tree diseases The disease incidence, severity and distribution are directly related with fungi, bacteria, viruses and other microorganism infections.The drought or typhoons being extreme weather conditions can destroy large number of forest trees directly through overwhelming their physiological capacity and structural power. Expected alternations in climate reacted with the increasing pathogen stress and lack of fire of invasive species produced conditions favourable for several plant diseases of forest. The patterns wood decay rates by forest fungal species also change and have potential to effecting carbon cycles in the forest( Frankel, 2008).
In Western North America conditions like changes in weather extremes, precipitation and warming are effecting diseases of forest tree. The following instances deals the entire range from purely abiotic factors drought related decline (Alaska yellow-cedar decline) and through Dothistroma septosporum- red band needle blight of pine which is a weak native pathogen and through an aggressive but non native pathogen sudden oak death due to Phytophthora ramorum which are described below.
Alaska yellow-cedar decline- Earlier melting of snow exposes shallow fine roots to colder temperatures which produces spring freeze injury in Alaska destroying millions of Chamaecyparis nootkatensis (D. Don) Spach –yellow cedar (Hennon and D’Amore 2007, Hennon and Shaw 1997). The best instance of climatic impacts on a forest tree are the severe mortality of yellow cedar in up to 1000 kilometers in the northern Pacific coast of North America. The reasons of tree mortality were reduced basically due to two main causes such as soil drainage and snow depth.This is applied as a model for future and present suitability for cedar habitat (Hennon et al.,2012).
Red band needle blight (Dothistroma septosporum)- There was mortality of British Columbia plantations and mature stands of lodge pole pine (Pinus contorta Dougl. ex Loud.)through red band needle blight. The mortality was adjacent to places covered by Dendroctonus ponderosae (mountain pine beetle).The increase of precipitation in summer was the main cause of disease outbreak which is beyond the limit of other recorded weather patterns previously(Woods et. al 2005).
Sudden oak death (Phytophthora ramorum)- The extreme weather events are the causal agents of sudden death-related tree mortality of oak.The rate of sudden oak death mortality in in California and Oregon increase abruptly and subside.This pattern was driven due to heavy rains that extended wet weather in warm periods,creating optimal conditions of infection conditions. Infected plants face a reduction in capacity to manage water.It survives till high temperatures exists and extended up to dry periods.This overwhelms vascular capability of trees finally converting in death. This pattern of Two cycles was recorded in California: 1998-2001 and 2005 -2008 (Frankel 2007). The Bay Area place faced an all time record up to 25 rainy days during March 2006.This is followed by rain in July that is three above months of longest string of hot weather ever recorded.
During survey in Gurgaon and its suburbs, white flowered Plumeria acutifolia Poir trees of apocynaceae family have been found wilting. Frequent surveys showed 10-15% wilting in Gurgaon and wilting incidence was found alarming in IMT, Manesar. It caused total wilting and death of trees one after another in a row (Fig 3a,b,c.). Wilted P. acutifolia were observed in all age groups which showed yellowing of leaves starting from margins, then complete yellowing of old and even young leaves and finally death of the plant in 3-4 years. This was the first record of Acrophialophora levis causing wilt in this plant (Kumar et al.,2016).
Coleosporium sp causing rust infection of young Plantations of Plumeria obtusa and P. hybrida at various locations of Gurgaon from March,2014 to March,2015. (Fig 4)which resulted in leaf drying and death.. The rust pustules diameter on leaves was between 0.5-3.0 mm.But none were seen in the flowers or stem. Microscopic investigations resulted presence of the uredia, formed through extending mycelium in a crosswise direction which arised through rupturing of lower epidermis. There was absence of fruiting structures, telium, aecium or spermatium. Both young and mature leaves showed susceptibility to the pathogen. This caused chlorosis, necrosis and fall of premature leaf (Kumar and Khurana ,2016a).
Aecidium sp. (Pucciniaceae) on Cordia dichotoma G. Forst was also investigated for the first time in Panchgaon, Gurgaon Haryana was observed in February March 2014-16 having oval to rounded, chlorotic lesions measuring 4–14 mm in diameter on living leaves.Aecia structure were cupulate,gregarious,yellowish,erumpent having peridium and lacerate having recurved margin(Kumar and Khurana, 2016b).The best case of fungal mycosis is cankers disease due to Geosmithia morbida which is carried by the walnut twig beetle. This destroyed the eastern Juglans nigra( black walnut) in certain places of United States(Jans,2016).
Calotropis procera (Aiton) W.T. Aiton. (Asclepiadaceae) commonly known as Madar or’Aak’ is a medicinally important wild shrub native to India .It is useful in treatment of a number of illnesses including dysentery,intermittent fevers, cold, cough, and asthma. We observed a serious leaf spot disease of madar growing on wasteland near about AUH in Panchgaon, Manesar- Gurgaon (Haryana) in years since January 2014. In January February 2017, this leaf spot was on almost every plant in the vicinity. Disease incidence was greater than 90% and caused extensive abscission of leaves. Symptoms on infected leaves were first observed in end of October to November of each year as small, circular spots with large yellow to dark brown halos on both sides of the young and mature/old leaves. The size of spot enlarged gradually. Soon attained irregular shape or it remained circular having concentric rings or zones. This is yet another record from Aravali Hills near AUH, Gurgaon (Kumar and Khurana,2017a).
A leaf chlorosis, reddening and distortion was observed on naturally growing plants of glue berry- Cordia dichotoma at various places near Panchgaon(Manesar), Gurgaon since March 2014. This was confirmed as Taphrina sp. based on morphology of asci and ascopsores. This was the First report of Taphrina sp. causing leaf distortion and reddening in C. dichotoma. (Kumar and Khurana 2017b). Drought related decline- The Forest plants stressed by abiotic factors such as drought,have least capacity to survive under in climatic stress (Winnett 1998). There was worst drought in California.This resulted over $2.5 billion damage (Keeley et. al 2004, Kliejunas et. al.,2008). The drought of New Mexico and Arizona caused a severe loss of Pinus edulis Engelm. (pinyon pine) around 12 000 km2 in the Southwest (Breshears et al., 2005).