*2.3.2 National level*

Cultivating cotton by adopting closer spacing with the available cultivars and with those having short branches was conceived and implemented in India since sixties of the 20th century. Visits, exposures, dialogs and discussions could improvise the learning and the team's visit to Brazil had sown the idea of researching on High Density Planting System (HDPS) and the churned idea was implemented by reorienting research through All India Coordinated Cotton Improvement Project (AICCIP) and through other schemes like Technology Mission of Cotton (TMC) or National Food Security Mission (NFSM) in India [42]. It is reiterated that the success of HDPS at varied locations solely depends on the availability of genotypes, appropriate spacing and nutrition for adopting more plants per hectare to achieve more productivity per unit area and sound pest management criteria. This necessitates the evaluation of available genotypes in varied spacing and nutrition level to the incidence of insect pests. As farmers tend to grow more Bt which are normally of spreading in nature, evaluation of both Bt and not Bt compact genotypes for

their suitability to HDPS is the need of the hour. The adoption of HDPS along with better genotype and fertilizer management is a viable approach to break the current stagnation of yield.

More the synthetic fertilizer application, especially nitrogen (N) fertilizer, more the serious insect herbivores occurrence and crop damage from these insects by reducing plant resistance, the concept which has been conceived clearly [43, 44]. Reducing fertilizer applications can reduce the production costs for cotton growers, as well as nitrogen (N) leaching into the soil and contamination of surface and ground water, but altered N fertilization may also affect pests and their natural enemies [45]. Occurrence of insects and their abundance are heavily dependent on the micro climate available in the system which is primarily based on the biomass production by the plants and their nearness (spacing). Hence, it is utmost important to study the pest dynamics under closer spacings as well as increased levels of nitrogen applications.

A study taken up using GSHV-01/1338 and GBHV-164 genotypes among others revealed their ability as promising genotypes of the region suited to high density planting system due to its compact nature [42]. At two levels of closer spacings (60x15 and 45x15 cm) against the normal spacing of 120x45 cm along with two increased level of nitrogen application (i.e. 125 and 150% of RDN), these two genotypes performed better. The studies were carried out in factorial randomized block design *Kharif* 2013–2014. Closer spacings (45x15 and 60x15 cm) attracted more thrips as compared to the recommended spacing (120x45 cm). The mean population of thrips was found significantly high on GBHV-164 than GSHV-01/1338. Higher dose of nitrogen application on crop (125 and 150% RDN) attracted more thrips as compared to 100 per cent recommended dose of nitrogen (RDN).

[46] by quoting a field experiment that was conducted to study the mean incidence of major cotton insect pests during two consecutive seasons *i.e*. during *kharif*, 2010–2011 and 2011–2012 at CICR, Nagpur under high density planting system (HDPS) using different genotypes of *G. hirsutum* with different spacings indicated that pest incidence was not altered by closer spacing. The main objectives of the work was to identify lines of *G. hirsutum* which have less infestation of major insect pests under HDPS system and to investigate whether the incidence is influenced by plant density. In 2010–2011, the minimum mean population of leafhopper was observed in NISC-50 (1.82 nymphs / 3 leaves /plant) which was grown at a spacing of 45x13.5 cm followed by PKV-0811 (1.91 nymphs /3 leaves/plant) grown at a spacing of 45x13.5 cm and these genotypes are significantly superior over the others. The injury grade was I in both NISC-50 and PKV-081 genotypes. The mean per cent square damage was low in CNH-120 MB (2.76%) followed by PKV-081 (3.82%), both being statistically on par with each other and significantly superior over other genotypes. The mean pink bollworm population was low on PKV-081 (2.53 larvae/25 green bolls). The lowest per cent locule damage due to pink boll worm was noticed on PKV-081 (8.48%). However, the performance of genotypes and geometry against all the insect pests in 2011–2012 was not significantly different leading to a conclusion that pest incidence was not altered by closer spacing.

[47] reported in a study undertaken during 2015–2016 on High density planting demonstrations (50) which were taken up in farmers' fields at varied close spacings (75x10 and 90x10cm) with available compact genotypes (Suraj and G.Cot.16) compared to normal spacing (120x45 cm) under Insecticide Resistance Management (IRM) umbrella in rainfed regions of Bharuch district. Aphids, thrips and leafhopper were found above ETL whereas whitefly and mealybug were found below ETL. The mean larval population of pink bollworm was 4.41 and 3.14 larvae/20 green bolls in Suraj and G.Cot.16 spaced at closed spacings respectively. The pink bollworm population was 2.51 and 2.68 larvae/20 green bolls in Bt-IRM and non IRM

#### *High Density Planting System of Cotton in India: Status and Breeding Strategies DOI: http://dx.doi.org/10.5772/intechopen.94905*

plots respectively. Suraj variety spaced at 75x10 and 90x10 cm required 4.21 and 3.33 sprays and G.Cot.16 spaced at 75x10 and 90x10 cm required 4.40 and 3.60 sprays against sucking pests and 2.37 and 2.38 and 3.20 and 2.40 sprays against bollworms respectively as against 5.00 and 5.60 sprays against sucking pests and 2.00 and 3.80 sprays against bollworms in Bt-IRM and Bt-Non IRM cotton respectively. These results suggest the need for excessive sprays in ultra closer spacing than the normal closer spacing for both the cultivars. The net return was found higher in G.Cot.16 HDPS at both the spacing (Rs. 22,966 and 17,456/acre) than the Suraj HDPS (Rs. 16,461 and 8235/acre). The net return for Bt-IRM farmers was higher (Rs.21527/ acre) than non IRM-Bt farmers (Rs. 17,919/acre). Thus, it has been concluded that HDPS offer viable option to increase productivity especially under rainfed region.

The cotton crop is attacked by 1326 species of insect pests throughout the world, of which about 130 different species of insects and mites found to devour cotton at different stages of crop growth in India. Among the bollworms, pink bollworm assumed major pest status in recent past [48]. The pink bollworm, *Pectinophora gossypiella* (Saunders), a pest which received more attention in almost all the cotton growing states of India (except Tamil Nadu as of now), is identified as the most destructive pest of cotton and causes 2.8 to 61.9 per cent loss in seed cotton yield, 2.1 to 47.1 per cent loss in oil content and 10.7 to 59.2 per cent loss in normal opening of bolls [49]. Locule damage was noted to an extent of 55 per cent and 35–90 per cent reduction in seed cotton yield has been reported by [50, 51] estimated the yield loss to an extent of 6525 MT annually.

Losses caused by pests vary by 10–30% depending on the intrinsic genetic factors and its rigidity in expressing the inherent resistance. Pests are supposed to evolve in a short and strategic cycle to circumvent the problems being arisen and judicious use of insecticides along with physical, biological control methods is the need of the hour. Ignoring pests can lead to complete crop failure. In the overall crop protection program under the National Agricultural Policy, The Government's IPM is a time-tested, eco-friendly approach, socially acceptable and economically viable that is widely accepted across the country. Appropriate control measures should be taken when insect populations cross the ETL [52].

#### **2.4 Diseases management**

High density planting which entails closer planting may have every chance of microclimate getting altered due to which the propensity of infectious diseases in cotton may also vary. The high density planting in cotton is a recent phenomena which opened avenues for research in various domains including plant pathology. The plant pathologists have been trying to understand the nexus between the incidence of various cotton diseases and the change in microclimate of the plant coupled with external atmosphere [53, 54].

The life cycle of pathogens is amenable for changes in line with the changes in plant canopy and the microclimate mediated through weather parameters. Space between plants and rows is bound to have a say in the mode of dispersal, the intensity of infection and the production of secondary inoculum of plant pathogens. Cotton, being a commercial crop, is no exception to this phenomena of infection and the high density planting in cotton need to be carefully contemplated taking into account the changed plant geometry and the corresponding incidence of cotton diseases. Despite the research on influence of high density planting in cotton on the incidence of diseases is in the nascent stage, an attempt has been made to take stock of striking developments in the management of important cotton diseases in the succeeding pages.

The major diseases of cotton which are prevalent in most part of the cotton growing countries in the world were reported to inflict a damage ranging from 10 to 30% and it may be more when favorable conditions prevail for the spread of the pathogens which culminates in cotton farmers spending huge cost to keep the biotic stress under control [55].

Fungal diseases are predominant in cotton followed by very few bacterial and viral diseases. The prominent bacterial disease which inflict major damage in cotton crop is bacterial blight, caused by *Xanthomonas citri* pv. *malvacearum* [56]. Abundant literature is available on major fungal diseases of cotton namely *Fusarium* wilt caused by *Fusarium oxysporum* f. sp. *vasinfectum*, *Verticillium* wilt caused by *Verticillium dahliae*, anthracnose caused by *Colletotrichum gossypii*, Ramularia gray mildew caused by *Mycosphaerella areola*, root rots caused by *Rhizoctonia solani* and *R. bataticola*, leaf blight caused by *Alternaria macrospora* and leaf spot caused by *Cercospora gossypina* [57–62]. The cotton leaf curl disease is the only virus disease documented in cotton which belongs to the genus Begomovirus and transmitted by insect vectors [63].

Plethora of studies were conducted for the management of cotton diseases which reported solitary or combination of management practices to control them. Besides chemical control, significant research work has been carried out on the biological control of cotton diseases [64–67]. Similarly, there were prominent studies on use of plant extracts [68–70] and essential oil [71, 72] for the management of cotton diseases. Cultural methods [73] and organic amendments [74] also form part of the strategy to control cotton diseases.

In the recent past, several research studies have documented the efficacy of Endophytic bacteria [75] in suppressing the incidence of cotton diseases. Molecular level studies namely transcriptomic, proteomic and metabolomic studies [76–78] and studies on gene editing [79] were on the rise for the past two decades. As there are several methods and molecules have been designed for effecting the control of diseases, their role in containing the diseases that occur under HDPS is in infant stage as the genotypes which have been evaluated at Coimbatore were not found to have adequate disease expressions under HDPS.

#### *2.4.1 Soil borne diseases*

Soil borne fungal diseases of cotton namely damping off, root rot and wilt have been reported to cause extensive damage in cotton crop. Juxtaposing chemical control with biological method, the latter was found to be effective which is evidenced from the finding of [80–82] who reported that the combined application of *T. harzianum* and *P. lilacinus* showed the best result by inhibiting the growth of pathogen than alone. A recent study of [83] reported that Trichodel®, based on *Trichoderma* spp., reduced the incidence and severity of wilt caused by *F. oxysporum* f. sp. *vasinfectum*. Besides, a score of agronomic practices namely fine tilth of the soil, adjusting sowing season, crop rotation, soil solarization, amending soil for altering pH of the soil and use of resistant varieties have been reported to reduce the incidence of soil borne diseases. Biological control of *V. dahliae* in cotton with a mixture of lignin and *Trichoderma viride* [84] has been reported. Thus, biological control of soil borne diseases is the viable option which had been arrived by various authors in the normal cotton growing situations. However, the same might hold good under HDPS also.

#### *2.4.2 Foliar diseases*

Among the foliar diseases, Alternaria leaf spot, gray mildew, boll rot, rust, anthracnose and bacterial leaf blight were reported in cotton and they were reported to inflict damage significantly. The chemical fungicides mancozeb (0.3%), propiconazole (0.1%), propineb (0.3%) were found more effective against

#### *High Density Planting System of Cotton in India: Status and Breeding Strategies DOI: http://dx.doi.org/10.5772/intechopen.94905*

*Alternaria macrospora*, propiconazole (0.1%) and copper oxychloride (0.25%) against *Myrothecium roridum* [85, 86]. Moreover, a decadal analysis of *Alternaria* occurrence among the various genotypes at Coimbatore indicated that Bunny Bt cotton, NCEHBT, Dhannu BGII and 1037 BGII genotypes were found to be more susceptible and the disease incidence ranged from 0.5 to 10.53 PDI compared to the types which are resistant/field tolerant. In addition, the sowing taken up during 29th–30th Standard Meteorological Week (SMW) resulted in lesser incidence of the disease irrespective of the cultures evaluated [87].

Among the biocontrol agents studied, *Pseudomonas fluorescens* strains and *Bacillus subtilis* and the botanicals derived from *Azadirachata indica*, *Lantana camera*, *Calotropis procera*, *Ocimum sanctum*, *Allium cepa* and *Allium sativum* have been reported to significantly reduce the mycelial growth of the pathogenic fungus [88]. The methanol extracts of *Polyalthia longifolia* and *Terminalia chebula* and chloroform extract of *Zingiber officinale*, *Datura alba*, *Moringa olifera*, *Azadirachta indica* and *Syzgyium cumini* have showed significant biological control of cotton bacterial blight in greenhouses and in fields [89, 90]. This indicates that principles available in various plants are having sizable influence in containing the growth of disease causing micro organisms.

## *2.4.3 Viral diseases*

Among the viral diseases infecting cotton, cotton leaf curl virus and tobacco streak virus are important. The TSV disease was reported to be spread through mechanical means, infected seeds and through thrips species. Parthenium, a widely distributed and symptom less carrier of TSV, plays a major role in perpetuation and spread of the disease [91–95].

A study carried out by [96] uncovered the application of *Bacillus* species which possess diverse anti microbial peptide (AMP) genes which are responsible for the biosynthesis of antibiotics like iturin, bacilysin, bacillomycin, fengycin, surfactin, mersacidin, ericin, subtilin, subtilosin, and mycosubtilin in curtailing the infection of TSV. Genetic Engineering studies to evolve transgenic cotton using an antisense RNA approach [97] could be a potential option for managing the disease. Interestingly, transgenic cotton plants that over express miR166 also show potential in reducing *Bemisia tabaci* populations and, more importantly, the spread of whitely transmitted plant viruses [98, 99]. Gene editing technology *i.e.,* CRISPR/Cas9 system has recently been used to confer molecular immunity against several eukaryotic viruses, including cotton DNA geminiviruses [100].
