**2. Indian cotton scenario**

About 59 per cent of the raw material requirement of the Indian textile industry is met by cotton. It plays a major role in sustaining the livelihood of An estimated 5.8 million cotton farmers' livelihood is sustained by cultivating cotton. Besides, this crop engages 40–50 million people in one or the other related activities. As seen, the area under cotton in India is also tremendous which is around 13.40 million hectares. Among the 53 species of *Gossypium* available, Indians cultivate all the four species of cotton namely *Gossypium arboreum* and *herbaceum* (Asiatic cotton), *G. barbadense* (Egyptian cotton) and *G. hirsutum* (American Upland cotton) with *G. hirsutum* being cultivated over the entire Country. It is about 88% of the hybrid cotton being cultivated in India belongs to *hirsutum* type and almost all the *Bt* cotton hybrids belong to G.*hirsutum* type*.*

Cotton is grown in all the three different agro-ecological zones of India *viz.,* Northern, Central and Southern zones. Nearly 70 percent of the crop is cultivated under rainfed condition in the Central and Southern regions of the country. Among the cotton producing states, Maharashtra is the largest producer with an area of 38.06 lakh ha followed by Gujarat (24 lakh ha) and Telangana (17.78 lakh ha). In India, the production of cotton is recorded in bales which are of 170 kg. The production is highest in Gujarat with 95 lakh bales followed by Maharashtra (89 lakh bales) and Telangana (59.50 lakh bales). Karnataka stands first in productivity with 769 kg ha−1 followed by Andhra Pradesh (719 kg ha−1) and Rajasthan (692 kg ha−1) [2].

Majority of the cotton produced in India is derived from nine major cotton growing states and these States fall under three diverse agro-ecological zones.


In addition, cotton is also grown in the States of Tamil Nadu and Odisha. Recently, cotton is also being cultivate in small scale in non-traditional States such as Uttar Pradesh, West Bengal, Tripura, etc. Nevertheless, India is the largest producer cum leading consumer of cotton in the World. It's very clear now that albeit having higher area under cotton, the productivity of cotton is very low compared to many of the Countries which warrants attention mainly on developing newer genotypes that would yield better on higher management condition. Strategies that could maximize the per unit area yield in cotton would include

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


Primarily, the productivity enhancement in any crop depends on the development of suitable genotype and cotton is not an exception. Many of the wild species available in the crops are exploited for transferring the segments (QTLs) that harbor pests and diseases resistance *vis-a-vis* high yield. Though about 53 species of *Gossypium* are available including the four cultivated species, only very few diploid and tetraploid wild species of *Gossypium* are crossable with the cultivated species. Among the species of *Gossypium*, seven species are with AD genome measuring 2400 Mb genome size, three species with A genome (1700 Mb), four species with B genome (1350 Mb), three species in C genome (1980 Mb), 13 species with D genome (885 Mb), seven species in E genome (1560 Mb), one species belonging to F genome (1300 Mb), three species under G genome (1785 Mb) and 12 species under K genome (2570 Mb) [3]. Since cotton is being available in the field for more than 5–6 months before harvest, per day productivity of the crop also receives much attention.

Another statistical prediction provided by Dr. M. V. Venugopalan of CICR, Nagpur [4] is that the cotton productivity during 2018–2019 would be the lowest despite the fact that almost 90% of the farmers have adopted the state of art BG II hybrids. This had been exclusively due to the increase in cost of cotton cultivation from Rs. 2233/q of seed cotton in 2002–2003 to Rs.4803/q in 2015–2016, mainly due to increase in labour wages and increased use of inputs like fertilizers and pesticides. Considering these facts, primary aim of the plant breeders has to be in designing a genotype that would fit for the given situation.

Moreover, the present day hybrids put forth biomass enormously and are of speed and spread growing in nature. Thus, the ratio of bolls to biomass if worked out would be much lesser. For having a match between the growth, water requirement, duration, yield, per unit and day productivity etc. a system was arrived at by the Central Institute of Cotton Research, Nagpur which is High Density Planting System (HDPS) with early maturing, semi compact genotypes for realizing higher yields with low production costs under rainfed condition primarily. The main tenets of this proposition covers tailoring a genotype suiting to high density planting (more than one lakh plants per hectare), its uniformity in boll development, maturation and bursting, its adoptability to the given condition and efficiency in the nutrient utilization etc.

In the forth coming discussions, let us see about the genetic, agronomic and plant protective interventions that would help in developing a suitable genotype fitting to HDPS.

#### **2.1 Genetic interventions**

#### *2.1.1 Genetic enhancement*

The term "enhancement" was first used by [5] for defining the transfer of useful genes from exotic or wild types into agronomically acceptable background, preferably a cultivar of choice. This term of enhancement was later [6] rechristened as pre-breeding

or developmental breeding to describe the same activity. Thus, having varied terminologies basically refer to the transfer or introgression of genes or gene combinations from unadapted sources, mostly the wild sources into the breeding materials, preferably an adapted background [7]. Normally, genetic enhancement is complementary to that of traditional breeding. However, these activities, as name suggests, form the base of any plant breeding programme where the gene transfer from wild species /related species is targeted. Thus enhanced germplasm can be more readily used in breeding programmes for cultivar development. Thus, pre-breeding qualifies as prior step of sustainable plant breeding which normally starts with identifying a useful character in unadapted or wild genotypes, capturing its genetic diversity and extracting the genes/QTLs that govern these variations for exploitation. Thus pre-bred materials may also be an intermediary with a value addition which could be further exploited.

Normally, wild species are exploited for transferring traits related to the improvement of yield, quality, pests and diseases resistance. In cotton, for altering the plant types, the wild species are not that much useful for the reasons that most of them are perennial with spreading habit. Hence, for breeding an ideal genotype with less/shy branching, zero monopodia, minimalistic bolls with uniform weight, luster, shape and bursting etc. which would also suit mechanized cultivation, exploring the available variability among the germplasm must be the pre-requisite.

Research on HDPS on cotton gained momentum under the leadership of ICAR – Central Institute for Cotton Research, Nagpur in 2010. Shortly thereafter, in 2012, the All India Coordinated Cotton Improvement Project (AICCIP, now AICRP on Cotton) started a separate trial on the evaluation of compact genotypes for HDPS under rainfed and irrigated situation to facilitate the release of compact genotypes suitable for HDPS. Variety CSH 3075 was the first cotton variety released for HDPS in India. [4]. Subsequently, research got momentum and Tamil Nadu Agricultural University (TNAU) has also released two varieties *i.e.,* TCH 1705 as CO 15 and TCH 1819 as CO 17 for HDPS. Cotton CO 17 has been performing well under rice fallow conditions of Cauvery Delta Zone of Tamil Nadu (**Figure 1**).

#### *2.1.2 Varietal evaluation*

A high yielding *G.hirsutum* variety CO 15 developed from Department of Cotton, Centre for Plant Breeding and Genetics, Tamil Nadu Agricultural

**Figure 1.** *HDPS cotton (CO 17) being cultivated at farmer's holding.*

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

University, Coimbatore was evaluated in All India Coordinated Cotton Improvement Project trials on cotton during the year 2012–2013. This culture registered a significant seed cotton yield (2346 kg/ha) which is 111.2% increase over the local check Suraj (normal spacing) (1111 kg/ha). In south zonal trials, during 2013–2014, CO 15 (3582 kg/ha) out yielded the zonal check Suraj (3158 kg/ha) by 13.4% and stood at third place and during 2014–2015 registering 5.3% increased yield (2378 kg/ha) than the zonal check Suraj (2259 kg/ha). The seed cotton yield was maximum to the tune of 3226 kg/ha as against 2443 kg/ha of LH 2298 under.

60 x 10 cm. This culture is found to be fertilizer responsive in all the location. Increasing the spacing results yield loss in almost all the centres indicating its suitability for high density planting. It registered moderate resistance to Bacterial blight and Gray mildew. The overall performance (2012–2015) revealed its superiority in mean seed cotton yield (2807 kg/ha) as against the local check Suraj (normal spacing) (2146 kg/ha). The increase in kapas yield was 30.8% over local check. Besides high seed cotton yield, it possessed higher ginning out turn of 36.6% than zonal check Suraj (34.1%). This culture comes under the medium long staple category with 2.5% span length of 27.1 mm, fiber strength of 21.5 g/tex and micronaire value of 4.3. It can spin up to 30–40's counts.

Cotton variety CO 17 is a short duration compact plant type with synchronized boll maturity suitable for high density planting system (HDPS) released by the University during 2020. This culture was developed at Department of Cotton, TNAU, Coimbatore from the parental hybridization involving Khandwa 2 and LH 2220 followed by pedigree breeding. It matures in 125–135 days and possesses zero monopodia with short sympodial length and is highly suited for high density planting system. It recorded an average seed cotton yield of 2361 kg/ha which is 18.9% increase over the check variety Suraj (National check entry identified for HDPS). Culture TCH 1819 recorded seed cotton yield of 3427 kg/ha which was 21.7% increase over Suraj and 29.0% increase over MCU 7 under rice fallow condition. It recorded a seed cotton yield of 2051 kg/ha which was 13.8% increase over Suraj under summer irrigated conditions and also recorded 1604 kg/ha of seed cotton yield under winter rainfed which was 20.1% increase over the check Suraj.

It was also evaluated in All India Coordinated Cotton Improvement Project trials for two years during 2016–2017 and 2017–2018 across ten locations. It registered seed cotton yield of 1850 kg/ha which was 37.9% increase over Suraj. Adaptive Research Trials (ARTs) were conducted under three different cotton growing seasons *viz.,* rice fallow, winter rainfed and summer irrigated conditions during 2016, 2017 and 2018. It recorded the highest mean seed cotton yield of 4530 kg/ha which was 17.2% increase over the check Suraj under rice fallow condition. It recorded Upper Half Mean Length (UHML) of 27 mm with bundle strength of 26.9 g/tex. It can spin upto 40's counts.

Considering the descriptors of these two varieties, few features can be noticed in common and they are short intermodal length with lesser distance of boll from main stem, bolls of 4–5 g in weight and lesser plant surface coverage of not exceeding 0.25 m<sup>2</sup> ground area and synchronized maturity. Research work undertaken at the Department of Cotton, TNAU during one decade has resulted in identifying these genotypes which could exclusively fit in HDPS. Moreover, research being undertaken in the entire country had resulted in the release of varieties which are meant for HDPS which are detailed (**Table 1**).

#### *2.1.3 Genetics of the traits governing HDPS*

Majority of the traits that define a genotype fitting for HDPS include shy branching, 10–15 bolls per plant, boll setting nearer to the main stem, boll of 4–5 g in


#### **Table 1.**

*Details of cotton varieties released for HDPS (courtesy: Central Institute of Cotton research, Regional Station, Coimbatore).*

weight, uniform in size and shape, completion of bursting of all bolls in 3–4 days time, medium to superior medium fiber length with appreciable strength, 120 to 125 days of crop duration for fitting into various cropping programmes. These traits have been extensively studied using the available germplasm and prominent crosses have been effected to identify the genotypes that would fit in HDPS. Studies taken at the Department of Cotton by effecting crosses with genotypes fitting with HDPS and heavy yielders have indicated that crosses CO 17 x CO 14 and TCH 1926 x RB 602 showed high *per se* performance and positive significant *sca* effect for single plant yield. The hybrids C -10-8 x GISV 310 and CO 17 x GISV 310 which involves compact lines showed high *per se* performance, positive significant *sca* affect and positive standard heterosis for single plant yield. The hybrid CO 17 x TCH 1926 had high *per se* performance and positive significant *sca* effect for number of sympodial branches per plant and single plant yield and *per se* performance for number of bolls per plant.

Another study was taken up at the Department of Cotton during 2018–2019 to assess the spectrum of variability realized from differently yielding compact hybrids. Among the 900 observed plants in F2 population, surface covers of 689 plants were recorded as lower than the check (CO 15). The crosses viz., 343–1-1 x CO 14, 343–1-1 x RB 602, TCH 1926 x RAH 1070 and CO 17 x RB 602 were identified as elite combinations as they had more number of individuals whose plant surface was considerably lower than the check (CO 15).

Effect of Okra Leaf Shape in HDPS:

Considering the bigger leaf lamina which is available with CO 17, more pronounced leaf hoppers problem had been observed and breeding research to develop plants with HDPS traits along with okra leaf type had been the tailored programme which was started to function from 2015 to 2016. The okra leaf shape character, on an average in varieties over locations, caused a significant reduction in the incidence of boll rot in comparison with normal leaf cotton [8]. Altering, rather reducing the leaf lamina was significantly associated with an increase in yield, earliness, lint percentage and micronaire value, and a substantial increase in fruiting rate. However, it was also observed that the okra leaf shape had no effect on boll weight and fiber related attributes *viz.,* fiber length, fiber length uniformity, or fiber strength, but with a reduction in fiber elongation and total leaf area.

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

At present in the Department of Cotton, work initiated on the development of compact plant type with okra leaf shape suitable for HDPS resulted in two F2 populations viz., TCH 1819 x PBH 115 and TCH 1819 x F 2382. Okra-leaf types of the upland cotton have the potential to be competitive to the normal-leaf types in yield and fiber quality, in addition to its potential resistance to insect pests and drought. In cotton, okra leaf type plants confer resistance/non-preference against insect pests. Form these two F2 populations, a total of 85 single plants were selected for compactness with okra leaf. Reciprocal crosses of above two cross combinations were also made. Forwarding these progenies would help in identifying compact plant types with the okra leaf type.

Prominent feature being considered for HDPS is that the genotype must have occupy an area of <0.25 m2 on the ground and invariably possesses the traits like optimum plant height plant (around 100 cm) with shorter sympodia, shorter intermodal length with lesser distance of boll from main stem. Albeit the fact that HDPS was worked out for rainfed eco system, it fits well in the irrigated scenario also.

#### **2.2 Agronomic management and interventions**

In India, though the area under cultivation of cotton is higher, the seed cotton yield per unit area is very low compared to many other cotton growing countries in the world. The primary factors that attribute for this low realized yield besides the non-availability of choices of genotypes is the low plant population density. Various techniques like maintaining suitable plant density, use of optimum dose of fertilizers, growth regulators etc., are being suggested to overcome these constraints in cotton production. The optimum level of cotton productivity would, however, depends on the plant type being grown. The present day cotton genotypes are of long duration (180–200 days), late maturing, tall growing with spreading nature leading to bushy appearance besides with lesser number of bolls compared to the crop canopy. They also require wide spacing for the expression of the crop resulting in the production of netted canopy resulting in various problems in taking up plant protection measures, machine picking, and inefficiency in trapping of solar energy, physiological efficiency and harvest index.

Because of longer duration, these varieties require more number of pickings, as a result, cost of cotton cultivation upsurge especially owing to manual picking which warrants increased labour and fluctuating prices resulting in lesser realistic income. The availability of labour for clean picking is also a serious constraint. At present, in India, entire cotton is picked manually which is labour intensive and is becoming expensive day by day. About 30 per cent of world cotton being produced in Australia, Israel and USA and other developed countries are picked using machines which were sown as per the requirements of the machine. Such picking through machines would result in "Machine maximum, Man minimum" in cultivating cotton which will not only minimize cost of cultivation, but also reduce the dependency on labour. Machine picking esseentially depends on cultivation of cotton genotypes having short stature, earliness, compactness, sympodial growth habit and synchronous boll opening. Under these circumstances, compact cotton genotypes are ideally suited. They offer great scope for reducing not only row width, but also spacing between the plants in a row.

#### *2.2.1 Ultra narrow row (UNR) planting of cotton*

Over the last few decades, many cotton growing countries like China, USA, Australia, Brazil, Uzbekistan and Greece were able to enhance cotton yields by increasing the planting density. The planting geometry, in general adopted varies from 8 to 10 cm distance between plants in a row with the row spacing ranging from 18 to 106 cm, ideal being worked out to 100 cm at our conditions. This planting system is referred as narrow row (NR) if the row-to-row spacing is less than 75 cm and ultra-narrow-row (UNR) if the spacing is less than 45 cm. Currently in India, depending on the local conditions, hybrid cotton is planted at row spacing ranging from 90 to 120 cm and plant spacing ranging from 30 to 90 cm resulting in 15,000 to 25,000 plants/ha. In HDPS, short duration, semi–compact cotton varieties are planted at populations ranging from 1.1 lakh to 2.45 lakh plants/ha by planting at a distance of 45–90 cm between rows depending upon the soil type and growing conditions and 10 cm between plants in a row. It aims to establish around 7–8 plants/m row length. The objective is to limit the boll number to around 10/plant, maximize the number of bolls/unit area and realize high yield in the shortest possible time. If the number of bolls/plant is few, the fruiting window (or flowering period) is short (4–5 weeks) and the plant matures early, producing fibers with good quality.

Ultra narrow row (UNR) cotton production is considered as a potential strategy for reducing production costs by shortening the growing season [9]. By cultivating the genotypes that would fit for UNR, it provides the scope for increasing per unit area of plants *vis-a-vis* the productivity. Being shorter and earlier to mature, these genotypes under UNR provides scope for double cropping and mechanical harvesting. Since the number of bolls are less with uniformity in maturation and bursting, these compact types require few pickings only. This results in savings of labour cost as well as seed cost as it provides farmers an opportunity to reuse the varietal seeds for few sowing seasons.

Adoption of HDPS amicable compact and early maturing cotton varieties offer an alternate to sustainable production at decreased production cost under Indian condition. However, availability of more determinate cultivars, more efficient options of weed control and insect pest management (including transgenics), growth regulations to modify morpho frame, planting and harvesting equipments etc., has made high density cotton planting system popular in several countries. The concept on high density cotton planting, more popularly called Ultra Narrow Row (UNR) cotton was initiated by [10] and this concept has been one of the most researched topics during the last 15 years. Availability of early maturing, compact sympodial plant types with more fruiting bodies closer to the main stem is a prerequisite for successful HDPS.

#### *2.2.2 Planting density*

Theoretically, higher planting density ensures earlier crop canopy cover, higher sunlight interception leading to higher and earlier yields at reduced cost. The obvious advantage of this system is earliness [11] since UNR needs less bolls/ plant to achieve the same yield as conventional cotton and the crop does not have to maintain the late formed bolls till maturity. In general, it was observed that lower plant densities produced higher values of growth and yield attributes per plant, but yield per u--nit area was also higher with higher plant densities [12–14]. Fertilizer and pest management are important consideration for increased yields under high density planting system. Changes in plant density modifies the microclimate and this may alter the incidence of pests and diseases as well [15]. Studies taken up using the genotypes AKH 081,Suraj and NH 615 under HDPS revealed that these entries could yield better at 60 x10 cm spacing under medium depth soils with a planting density of 1.66 lakh plants per hectare on broad bed furrow (BBF) with 125 per cent of recommended fertilizers (75:37.5:37.5 NPK + 2.5 Zn kg/ha) along with a foliar spray of 1% urea and 1% magnesium sulphate at boll development stage [16].

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