Identification And Control Of Strawberry Root And Stalk Rot In Iraq

Strawberry (Fragariae ananassa Duch.) is one of the most economically important crops worldwide. It is grown under a wide range of climatic conditions as wild and cultivated plants producing small fruits. Strawberries are appreciated worldwide for their unique flavor, importance as a source of macronutrients and beneficial dietary compounds (Bianco et al. 2009) with benefits on neurodegenerative and cardiovascular (Bombarely et al. 2010). 

Strawberry plants reported to be infected by several soil borne pathogens causing root rot and crown rot (Fang et al., 2011a; Fang et al., 2012). Black root rot is a complex disease caused by one or more of fungal pathogens, including Fusarium oxysporum ( Juber et al.,2014 ), Macrophomina phaseolina (Hutton et al. ,2013) , Phymatotrichopsis omnivora (Hu, 2012) , Pythium spp. (Abdel-Sattar et al.,2008), Phytophthora spp. (Mingzhu et al., 2011)and Rhizoctonia ( Fang et al., 2013). These pathogens can cause crown rot and root rot disease to strawberry either individually or in combinations. Rhizoctonia spp. are soil-borne pathogens cause black root rot disease. These pathogens may be predominant in soils with high clay content. This complex disease is characterized by feeder rootlet killing, deterioration and blackening of the main root system, and a decline in vigor and productivity of the plant sand causing damage to the host and considerable reduction in the yield (Abdel-Sattar et al;2008, Fang et al.,2012b; Ceja-Torres et al., 2014) . 

The infected plant are less vigorous and produce fewer runners black root rot will exhibit one or more symptoms on roots. Root system is smaller than in normal plants. Lesions on the main root are darker than other root parts. Feeder roots with dark zones or lesions. All or part (usually the tip) of main roots killed. A cross-section of a dead root shows it is blackened throughout (Ullio, 2004). Root rot of strawberry caused by binucleate fungus Rhizoctonia fragariae Husain and McKeen or R. solani Kühn is a serious threat to commercial strawberry production worldwide. It is associated with severe economic losses, like those have been reported in Japan, Italy and Australia (Matsumoto and Yoshida ;2006; Manici, Bonora 2007 ; Fang, et al, 2011) Disease caused by Rhizoctonia spp. is difficult to manage due to the soil-borne nature and wide host range of Rhizoctonia spp. (Ohkura et al, 2009) . Phymatotrichopsis omnivora is one of a devastating soil borne ascomycete .This pathogen infects the roots of over 2,000 different species of plants and resulting in a rapid plant wilting and death causing significant economic losses. It was reported to destroy crops grown in the southwestern United States and northern Mexico (Gaxiola et al., 2010; Uppalapati et al., 2010; Ping Hu, 2012; Arif et al., 2014). Symptoms of root and crown rot are associated with wilting of some leaves manifested on some strawberry plants rots. 

Fungicides commonly used, such as Rizolex and Tachigaren are highly specific against R.solani (Abd-El-Kareem et al., 2004 ; Hameed ,2008 ; Fayadh et al., 2008 ; El-Morsi , and Mahdy.2013) and Fusarium oxysporum f. sp. fragariae (Juber et al.,2014) respectively. Growth regulators, chemical fertilizers and pesticides have extensively been used to increase yield in agriculture. Plant-Growth-Promoting Rhizobacteria (PGPR) could be used to replace the chemical products (Kawahara et al., 2006 and Walters et al., 2013). 

The use of such chemicals may cause environmental pollution problems, affect animal and human health, destruction of natural biological communities and modify natural nutrient recycling (Karuppiah and Rajaram, 2011). 

PGPR represent a wide range of rhizosphere- inhabiting bacteria which stimulate the growth of host plant through different mechanisms of actions (Zaidi et al., 2009; Martínez-Viveros et al .,2010 ; Karthikeyan and Sakthivel 2011; Ahemad and Kibret, 2014; and Noumavo et al., 2015). These mechanisms can be active simultaneously or independently at different stages of plant growth. Among these, P-solubilization , biological nitrogen fixation, improvement of other plant nutrients uptake, and phytohormone production like, indole-3-acetic acid , gibberllins, and cytokines are some of the regulators that profoundly influence plant growth (Kloepper et al.,2007 ;Bhattacharyya and Jha,2012; Mohite, 2013; Noumavo et al., 2015). It was found to produce ammonia, vitamins and also shows biocontrol activities like HCN and siderophore production ( Woyesa and Assefa 2011; Paul et al., 2014). Different PGPR including associative bacteria such as, Azotobacter, Bacillus, Pseudomonas, Enterobacter have been used for their beneficial effects on plant growth (Shoebitz et al., 2009; Ordookhani and Zare,2011; Sharafzadeh,2012;Matloob and Juber, 2013; Noumavo et al., al., 2015).

Systemic acquired resistance (SAR) is the activation of plants defense mechanism leading to induction of systemic resistance to subsequent pathogens infection .Ascorbic acid (Preserve Pro) has been known to have many biochemical functions in most organisms. The role of Ascorbic acid in tolerance of plants to environmental stress has established much consideration (Khan et al., 2011). This phenomenon, that resistance of plant to pathogens can be enhanced by the application of various biotic and a biotic agent, called induce systemic resistance in plants (Sarwar et al ,2005 ;Abd-El Kareem et al ,2006 ;bd-El-Kareem et al, 2007) Ascorbic acid is an essential cofactor for α-ketoglutarate-dependent dioxygenases (e.g. prolyl hydroxylase hydroxylases). It is important for formation of covalent adducts with electrophilic secondary metabolites in plants (Tarber& Stevens, 2011). The photolysis of ascorbic acid appears to be affected by the concentration of active ingredient, pH, and viscosity of the medium (Ahmad et al., 2011). So the study was aimed to isolate and identify the causal agents of strawberry root and stalk rot and test some chemicals and biological agents as well as some specific fungicides to manage the diseases.