**5. Race concept in** *Fusarium oxysporum* **f.sp.** *lentis*

In order to devise strategies for conferring resistance against disease, it is important to have knowledge of pathogen variability and prevalence of particular races in the target environment. The pathogen populations are primarily characterized by its virulence analysis on cultivars carrying differential resistance genes. Many researchers have studied the pathogen variability based on their grown on different solid media and on the basis of their pathogenicity [63, 64]. Later, Pandya et al. (1980) has evaluated the line (Pant-406) against seven races proposed by Kannaiyan and Nene [64], and found it immune to race 5, resistant against races 3 and 6, and partially resistant against race 4 [65].

Belabid et al. (2004) has reported that all the 32 Algerian isolates of *Fol* under study represent a single race but differ in their aggressiveness on the susceptible line on the basis of virulence and vegetative compatibility [66]. In India, on the basis of disease reactions against seven lentil differentials, the isolates were grouped into three clusters [60]. In an another study based on genetic variability, the *Fol* isolates collected from north eastern Indo-Gangetic plains revealed two sub-populations groups [61]. Sallam and Abdel-Monaim (2012) have collected 10 isolates of *Fol* from different locations at Minia, Assuit and New Valley governorates, which were varied in their virulence [67].

Maheshwari et al. (2008) tested the effect of seven fungitoxicants against *Fol*. The results suggest that carbendazim was the most effective (5.6 mm) followed by captan (9.9 mm) and hexaconazole and diniconazole for reducing the fungal growth [76]. Several studies were carried out for determining the concentration of the fungicides to control the growth. The results suggest that the best fungus control was observed at highest fungicidal concentration (100 ppm) with benomyl followed by thiophanate methyl, second most effective at 100 ppm concentration [74, 77]. In Syria, seed treatment with benomyl-thiram did not affect Fusarium wilt incidence [78].

Fusarium Wilt: A Killer Disease of Lentil http://dx.doi.org/10.5772/intechopen.72508 125

Biological control is known to be the best and effective method, against soil-borne pathogens. This method has many advantages such as environment friendly, cost effective and extended plant protection. Many fungal and bacterial species like *Pseudomonas*, *Trichoderma* and *Streptomyces* have antagonistic effect on Fusarium wilt of lentil. Among them *Trichoderma* species are been extensively used as bio-control agent against soil and seed-borne diseases [74]. A study revealed that the seed treatment with *Gliocladium virens* + *P. fluorescens* + carboxin and *Bacillus subtilis* + carboxin + *T. harzianum*/*T. viride*/*G. virens* have been found more effective in controlling Fusarium wilt incidence in lentil [79, 80]. In the recent study, two species of *Trichoderma* were employed against highly virulent isolate of *Fusarium* responsible for lentil wilt. The results revealed that *T. harzianum* was highly effective in controlling wilt

In an experiment conducted by Garkoti et al. (2013) observed significant reduction in disease incidence and maximum grain yield in field trials using 'Pant L-639' a popular cultivar against lentil wilt with *T. harzianum* + *Pseudomonas fluorescence* [81]. Similarly, in another report the result suggest that the disease severity was reduced with increased plant height with the combination of *T. harzianum* + *S. vermifera* [82]. Likewise, El-Hassan and Gowen (2006) has evaluated the formulation and delivery of the bacterial antagonist *Bacillus subtilis* against Fusarium wilt of lentil. The result reveal that the seed treatments with formulations of *B. subtilis* on glucose, talc and peat significantly enhanced its biocontrol activity against *Fusarium* compared with a treatment in which spores were applied directly to seed [83]. Additionally, several studies have also proved the importance of the organic material in reducing the disease incidence caused by plant pathogen like bacteria [84], fungi [85] and nematode [86] species.

The cultural control generally depends on date and depth of sowing and manipulation of agronomic practices [68, 87]. It is reported that delay sowing usually lowers the wilt incidence whereas compared with early sowing (end of July), late sowing resulted in low yield [88]. The most suitable dates vary according to the different production regions. Use of clean seed for sowing and use of fungicidal seed treatment can reduce contaminating inoculum sources. To prevent the crop from various diseases a proper depth (10–12 cm) of seed planting should be used [89]. Intercropping/mixed cropping is being suggested for reduced wilt incidence and increased crop yield. Haware (1982) suggested that deep ploughing and removal of infected trash can reduce inoculum levels of Fusarium wilt of chickpea [90]. Soil solarization is another way to minimize the disease incidence [91]. In order to control the lentil wilt pathogen, chemical amendments (Mn and Zn) and foliar application on lentil wilt is also recommended. The

disease in comparison to other isolate, when applied as a soil drench [74].

**7.2. Biological control**

**7.3. Cultural practices**

Altaf et al. (2014) have characterized 15 *Fol* isolates (Fol-1 to Fol-15) collected from nine district of Pakistan on the basis of their pathogenicity and morphology [68]. Recently, Pouralibaba et al. (2016, 2017) have identify seven pathotypes (1–7) of *Fol* on the basis of their different pattern of virulence on lentil genotypes. Fifty-two *Fol* isolates originated from Iran, Syria and Algeria were used in the study. The results suggest that the pathogen 7 was virulent on all the accessions under study and there was no correlation found between the pathotype and the geographical origin of the isolates. The study was further confirmed by analyzing histopathology pattern of infection on resistant/susceptible varieties by pathotypes 1 and 7, which suggests that lower disease index was measured with plants inoculated with pathotypes 1 but not with pathotype 2 [69, 70]. Further studies are required to identify region specific pathogenic races using differential lines for conferring resistance against them in the respective agro-climatic regions.
