Efficacy of new generation oomycete-specific fungicides on life stages of Phytophthora meadii and field evaluation through bunch spraying system

Highlights

• New-generation oomycete-specific fungicides were evaluated in-vitro and in-vivo.

• Semi-systemic Mandipropamid could be a potential alternative to BM in FRD control.

• Spraying of fungicides reduced 65–75% of disease with increased dry nut yield.

• Bunch spraying system could be adopted in arecanut to realize better FRD control.

Abstract

Fruit rot disease (FRD) of arecanut, caused by Phytophthora meadii, is an important fruit disease of this palm tree that resulted in huge economic losses to the growers in India. In recent years, the control of this disease has become a prime factor in the management of arecanut plantations. Though prophylactic sprayings of Bordeaux mixture (1%) along with other older fungicides are useful in reducing the disease severity. Hence, there is an urgent need for new generation molecules to combat FRD under field conditions. The present investigation was aimed at evaluating newer oomycete-specific fungicides in in-vitro on different life stages of Phytophthora and in-vivo through a Bunch Spraying System (BSS) from ground level. The pathogen was isolated, identified, and characterized from varied regions and one virulent isolate from each region was used. Out of the 11 fungicides tested, EC₅₀ for mycelial inhibition among isolates was lowest in Famoxadone + Cymoxanil. Similarly, the lowest EC₅₀ for sporangial production was recorded in Iprovalicarb + Propineb, Famoxadone + Cymoxanil, and Kresoxymethyl ranging from 210.70 to 517.87 mg mL^_1. The most effective fungicide for inhibition of zoospore release was Dimethomorph + Mancozeb which ranged from 406.81 to 565.80 mg mL^_1. Bunch spraying of fungicides such as Bordeaux mixture (1%), mandipropamid (0.5%), fosetyl-Al (0.3%), and a combination of metalaxyl-mancozeb (0.2%) from ground level had a significant (P < 0.05) effect against FRD. These fungicides were found most effective in reducing the disease up to an extent of 65–70% and which in turn increased the dry nut yield by 75–95% when applied twice compared to untreated control. However, a semi-systemic fungicide mandipropamid could be a potential alternative to the Bordeaux mixture for effective control of FRD under field conditions.

Introduction

The Palmae family comprises the major tropical tree species arecanut (Areca catechu L.) and is significantly grown in Southern and Southeast Asian countries viz., India, China, Indonesia, and Malaysia (Mitra and Devi, 2018). The acreage (7,30,823 ha) and production (12,08,938 tonnes) have increased over the last few years in India by contributing 49 and 50% respectively, (DASD, 2021). In addition, five million people in the country are solely dependent on arecanut for their livelihood, and it provides a major contribution to the national economy and foreign exchange (Amudhan et al., 2012; Chowdappa et al., 2014). Various researchers have demonstrated that betelnut has a wide range of pharmaceutical activities, anti-inflammatory, analgesic, and potential effects against various diseases (Gilani et al., 2004).

However, in the last two decades, crop intensification and expansion of arecanut plantations in non-traditional areas facing greater challenges of pest and disease occurrence (Balanagouda et al., 2021). Fungal diseases are considered the major threat to arecanut production which affects both qualitative and quantitative losses (Coleman, 1910; Saraswathy, 1994). In particular, Fruit Rot Disease (FRD) caused by an oomycetes pathogen Phytophthora meadii (McRae) has been the most devastating problem, resulting in significant economic losses (Koti Reddy and Anandaraj, 1980; Sastry and Hedge, 1985; Jose et al., 2008). The occurrences of FRD have increased recently in non-traditional areas in India, mainly due to the establishment of new plantations where the climatic conditions favored the FRD spread and development (Anandaraj et al., 1992; Balanagouda et al., 2022) and the growing of susceptible varieties. Therefore, disease management is a prime factor in maximizing productivity and providing economic viability across newly established plantations.

The use of fungicides remains a popular and efficient management method, despite the promotion of safe and environmentally friendly methods to battle FRD of arecanut. However, integrated disease management (IDM) approach involving phytosanitation and prophylactic application of Bordeaux mixture (1%) during the pre-monsoon period followed after 40–45 days has been recommended against FRD (Chowdappa et al., 2000; Gangadhara Naik et al., 2019; Narayanaswamy et al., 2017). Due to the increased occurrences of FRD during rainy days (June–September) and the limited usage of curative approaches, the spraying of copper-based fungicides has become a primary management option with advantage of higher efficiency, lesser input cost, and a lower risk of fungicidal resistance (Moral et al., 2014; Roca et al., 2007).

However, spraying of Bordeaux mixture becomes ineffective sometimes because of improper preparation and application, and the unable to spray at right time due to continuous heavy rainfall in FRD endemic areas. The major challenge faced by arecanut growers is the skill and risk involved in climbing trees during the rainy season (Anandaraj, 1985; Rao, 1962). Unfortunately, prolonged use of copper-based fungicides may result in the copper deposition in soils, which could have potentially harmful environmental and phytotoxic impacts (Komárek et al., 2010). Due to the recurrent use of relatively high doses of copper-based fungicides, the total copper concentration of the soil progressively increases over a period of many years (Giller et al., 1998; Brandt et al., 2010; Mertens et al., 2010).

Various management approaches might be used to prevent soil contamination by copper, including the optimum timing and method of fungicidal application, the use of oomycete-specific fungicides with higher efficiency against the pathogen, and others (Roca et al., 2007), the optimization of the fungicide application methods and times (Moral et al., 2014). In this context, many researchers and stakeholders have attempted to find out an alternative to the Bordeaux mixture and other copper-based fungicides for FRD management under field conditions (Gangadhara Naik et al., 2019; Pande et al., 2016). Fosetyl-Al in 1977, phenyl amides in 1977–1983; propamocarb in 1978; and dimethomorph in 1988, particularly single and multi-site fungicides such as dithiocarbamates, the quinone outside inhibitors, phenyl amides, and carboxylic acid amides, have all been developed and widely used in the management of Phytophthora diseases over the past several decades (Prathibha et al., 2016).

Single-site fungicides have been demonstrated to be quite efficient against FRD, but they were found to stimulate the development of fungicidal resistance against pathogen populations (Brent and Hollomon, 2007). Fungicidal resistance to Phytophthora has been reported in many other hosts across the countries (Heungens et al., 2016; Matheron and Porchas, 2000; Perez-Sierra et al., 2011; Turner et al., 2008; Vercauteren et al., 2010; Wagner et al., 2008; Samoucha and Cohen, 1984; O‘Brien and Weinert, 1995; Ishii et al., 2002) and many strategies were attempted to overcome this issue by synthesis and testing of newer fungicides (Matheron and Porchas, 2000; Prathibha et al., 2016).

Though many novel fungicidal molecules were assessed for the management of FRD in arecanut in recent years (Hegde, 2015; Lokesh et al., 2014; Pande et al., 2016; Ravikumar et al., 2019), one of the oldest recommended practices viz., the prophylactic spraying of Bordeaux mixture (1%) is still effective and popular among the arecanut farmers (Coleman, 1910). Research into alternate solutions to replace with copper-based formulations in FRD control has been encouraged recently in response to these limitations (Gessler et al., 2011). The most efficient and widely used fungicides against FRD are phenyl amides, particularly metalaxyl, which was first introduced in the 1970s as a systemic fungicide against oomycetes. Despite being effective, their regular use and prolonged application increase the risk of fungicide resistance in the population of the pathogen, especially for site-specific fungicides like metalaxyl, making the fungicide treatment less effective (Reuveni et al., 1980; Lambert and Salas, 1994; Gisi and Cohen, 1996).

To the best of our knowledge, the efficacy of newer generation oomycete-specific fungicides in the management of FRD has little investigated in India. Therefore, the current study was executed with aim of testing single and multi-site fungicides on different life stages of P. meadii under in-vitro conditions. To determine the pathogen baseline sensitivity, disease control efficiency, yield response, and cost-economic analysis under field conditions through a bunch spraying system.