ABSTRACT: hazards and development of fungicide resistant plant

ABSTRACT: Grape is one of the important commercial
fruit crops of India and is severely affected by downy mildew disease caused by
Plasmopara viticola which might cause total crop loss under favourable
conditions. Synthetic single site fungicides belonging to groups Quinone
outside Inhibitors (QoI), Carboxylic Acid Amides (CAA), phenyl amides (PA),
Cyanoacetamide-oxime and multi site fungicide copper base, thicarbate fungicide
alone or in combination with non systemic fungicides are commonly used for the
control of downy mildew in India. P. viticola has ability to develop
resistance against fungicides, so classify as high risk pathogen. Fungicide resistance
to QoI, CAA, and phenyl amide group fungicides in P.viticola were
detected in India and other vineyards of various countries. Therefore it is
necessary to assessment of efficacy of this fungicide for downy mildew control
in vineyards. Also study the efficacy of activated potassium salt of long chain
phosphorous 96% (APSP 96%) and chitosan were evaluated in vitro against P.
viticola and in field during the fruiting season of October to April
2014-15 at Nashik locations in Maharashtra against downy mildew. It was found continuous
10 application single site QoI fungicide azoxystrobin and kresoxim methyl, CAA
fungicide s showed the development and selection of resistant population in
vineyards while that the APSP 96%, chitosan significantly reduced downy mildew
incidence on leaves and bunches in grapes as compared to untreated control and
can be safely used in vineyards to prevent the buildup of fungicide resistant
population and effective disease management.

     Chemical
pesticides offer the primary solution for controlling plant diseases but
despite the great advantages they have brought to agriculture development but
continuous use of chemical fungicides has create major problems of
environmental pollution, human health hazards and development of fungicide
resistant plant pathogen. Therefore need to search to find a new alternative
method for disease management.

 

 

 

 

1.1.  
 INTRODUCTION

Downy mildew is an important disease in grapes (Vitis
vinifera L.) in most of the grape growing areas of India during warm
and wet conditions. It is caused by the obligate biotrophic fungus, Plasmopara
viticola (Berk. and Curt.) Berl & de Tony. In Maharashtra,
Andhra Pradesh and Karnataka the fruiting season is from October
to March and downy mildew infection during this period leads to significant
yield loss. The young shoots and inflorescence confront downy mildew infection,
whenever the foliage gets wet due to post monsoon rains or dew
formation. The disease is more damaging when the pathogen infects tender
inflorescence or young berries. Therefore control of this pathogen has
mainly through the use of chemical fungicides; conventionally fungicides
with various active ingredients are used for management of downy mildew
of grapes such as Quinone outside Inhibitors (QoI), Carboxylic Acid
Amide (CAA) phenyl amide (PA) etc. (ICAR-National Research Centre
for Grapes, 2013). But extensive use of fungicides might induce resistance in
pathogens against them, thereby reducing the efficacy of the products (Sawant et
al., 2016 and Sawant et al., 2017). P. viticola being a high
risk pathogen (FRAC Pathogen Risk List 2014), the tendency to develop
resistance is also high. Resistance to QoI fungicides have been reported in
India due to mutation of glycine to alanine in cyt b gene in P.
viticola isolates and made them almost nonfunctional in the management of
the disease (Sawant et al., 2016). The chemical pesticide are mostly
toxic, persistent, bio-accumulative and extremely harmful not only for human
health, but also for many living organisms Aktar et al., 2009.
Pesticides can contaminate environmental and also coming to natural water
source, causing direct and permanent damage to the ecosystem as well as their
residues can get enter the food chain of animals (Haria et al., 2013; Boobis
et al., 2008). The extensive use of these chemical pesticide killing
effect on non target organisms including of many pests’ natural enemies, such
as bumblebees, butterflies and bees and also cause the led to  the emergence of resistance phenomena in the
major crop pathogen (Van et al., 2003, Hollingworth et al.,2008)

     For this reason, researches
and many scientific workers have been focused in developing alternative methods
for managing crop diseases (Schmitt et al., 2009). A promising approach
consists in the use of natural compounds such as chitosan which have been
studied for their antifungal action and has very interesting for controlling
plant diseases (El Hadrami, 2010). It possesses a broad-spectrum antimicrobial
activity against plant pathogen and to induce numerous biological responses in
plants (Malerba and Cerana, 2016). Chitosan which is a naturally occurring linear polysaccharide
composed of randomly distributed ?-(1?4)-linked D-glucosamine (deacetylated
unit) and N-acetyl-D-glucosamine (acetylated unit) was selected for the study.
Chitosan has shown potential in control of plant diseases by inhibiting fungal
growth and development and can also elicit defense responses in plants against
various pathogens (Hadrami et al., 2010).

            Use of low risk
chemicals salts like potassium dihydrogen phosphate has been reported to control
several diseases (Saleh et al., 2007) including powdery mildew of
grapes. It is also known that phosphorous acid (HPO (OH) 2 and
fosetyl-Al or Aluminum tris O-ethyl phosphonate belonging to phosphonate group
of fungicides have multi target site to kill pathogenic fungi. They are
effective in controlling powdery mildew diseases in nectarine, mango trees and
downy mildew of grapevines (Reuveni and Reuveni, 1995; Wicks et al.,
1991). Keeping this at the backdrop, the present endeavour was use the chitosan
70 % DD and unique formulation of activated potassium salt of long chain
phosphorous 96% (APSP 96%) are seletected against of P. viticola and
assess its efficacy in a vineyard compares to fungicides used for downy mildew
management.