Development of hybrids and hybrid seed production of cole crops

Singh BK and Singh B. 2016. Development of hybrids and hybrid seed production of cole crops. In: Principles and Production Techniques of Hybrid Seeds in Vegetables (Singh B, Pandey S, Singh N, Manimurugan C, Devi J and Singh PM Eds). Training Manual No.  67, ICAR-IIVR, Varanasi, UP, pp 112-125.

Cole crops (Brassica oleracea) are a group of highly differentiated plants having 18 numbers of diploid and somatic chromosomes (2n=2x=18), and these are grown all over the world from arctic to tropical climatic conditions. The word ‘cole’ seems to have been derived from the abbreviation of the word ‘caulis’ meaning stem/cabbage/stalk, and it was variously spelt as Kale (English), Kohl (German), Kool (Dutch), Kal (Scandinavian), Kaali (Finnish), Kaol and Kol (Breton), Chou (French), Col (Spanish), Cal (Irish), Cavolo (Italian), and Couve (Portuguese); but usually, the word cole is more recognized in the literature worldwide. Variation within and between subspecies of B. oleracea, and present day cultivated cole crops (kale, broccoli, cauliflower, cabbage, kohlrabi and Brussels sprout) have evolved after a long time of natural/artificial hybridization, mutation, selection and domestication. All these forms are descended from a common kale like ancestor, the wild cabbage (B. oleracea L. var. sylvestris L.) which is still prevalent in the western and southern Europe, and North Africa (Table 1). Taxonomically, the cole crops belong to the order Brassicales (Cruciales), family Brassicaceae (Cruciferae), tribe Brassiceae, subtribe Brassicinae, genus Brassica, section Brassica and species oleracea (Singh 2015). Pachytene chromosome studies have shown that the B. oleracea is a triple tetrasomic for chromosome types B, C and E comprising the genome formula ABBCCDEEF with 6 basic genomes and showing some secondary pairing.

Table 1: Evolution of cultivated B. oleracea crops (Prakash et al. 2011, Singh 2015)

Probable sequence of evolution	Scientific name (B. oleracea var.)	Common name	Ancestor*
1	var. sylvestris L.	Wild cabbage	-
2	var. ramosa DC.	Thousand-head kale, branching bush kale	1
3	var. gemmifera DC.	Brussels sprout	2
4	var. dalechampii		3
5	var. costata DC.	Portuguese tree kale, tronchuda kale	1
6	var. medullosa Thell.	Marrow-stem kale	1
7	Intermediate between 6 & 8		6
8	var. gongylodes L.	Kohlrabi	7
9	var. sabauda L.	Savoy cabbage	5
10	var. capitata L.	White cabbage	9
11	var. capitata L.	Red cabbage	10
12	var. viridis L., var. sabellica L., var. palmifolia DC.	Kale and collards	1
13	var. italica Plencks	Broccoli, Calabrase	12
14	var. botrytis L.	Cauliflower (biennial)	13
15	var. botrytis L.	Cauliflower (annual)	14
16	var. botrytis L.	Cauliflower (Indian) or Tropical cauliflower	15

*Ancestors are represented by numerical letters (1 to 15) of evolution along with corresponding scientific name.

The economic parts used in the present day cultivated cole crops (cauliflower, cabbage, kohlrabi, kale, broccoli and Brussels sprouts) are stem, leaves, flower or modified forms which are named as curd, head, knob or leaf. The curd of cauliflower described as pre-floral fleshy apical meristem in which the lateral buds of shoot meristem are elongated and much branched, and apices of these branches form the structure of curd of which >90% abort prior to flowering. In cabbage, after the rosette stage, new leaves develop with shorter petioles and the leaves begin to cup inward to form head. It has normally smooth leaves, while savoy cabbage has attractive crinkled leaves. Moreover, kohlrabi, grown for its swollen/enlarged stem (knob) just above the soil line which has a short growing season in cool weather because it should be harvested when young and tender. In sprouting broccoli, the economic parts ‘head’ bears on terminal bud and ‘sprouts’ arise from axillary buds, are actually composed of fully functional flower buds of which relatively few abort prior to flowering. The Brussels sprouts, resemble as small cabbage, are grown for sprouts i.e. swollen axillary buds (2.5-5.0 cm in diameter) which arise along the stem of the plant. These axillary buds bear in a spiral arrangement around stem that may reach 65-125 cm in height. Moreover, kale and collards are non-heading cole vegetables grown mostly for tender leaves, used as greens or salad and decorative purposes too. Cole crops are rich in nutrients, including several carotenoids (beta-carotene, lutein, zeaxanthin); vitamins C, E, and K; folate; and minerals (Singh and Devi 2015). In addition, these cruciferous vegetables contain a group of substances known as glucosinolates which are responsible for the pungent aroma and bitter flavours. Many scientific studies have presented the health benefits of these vegetables. For bolting and flowering, most of the cole crops are generally performed on mature vegetative plants either in-situ or ex-situ at temperatures between 5-10 °C for 30-60 days i.e. vernalization other than tropical varieties/genotypes (Table 2). Two main climatic factors should be taken in to consideration while selecting the area for seed production of cole crops. The most important one is the temperature during winter which is critical for vernalization; and other one is the precipitation/rainfall during the season of flowering, seed maturity and harvesting.

Table 2: Low temperature requirements (5-10 °C for 30-60 days) for development of economic parts and flowering in cole crops

Crop	Development of economic/edible parts	Flowering
Broccoli, winter type	Yes	Yes
Broccoli, summer type	No	Yes
Broccoli, tropical type	No	No
Brussel sprouts	No	Yes
Cabbage	No	Yes
Cabbage, tropical type	No	No
Cauliflower, winter type	Yes	Yes
Cauliflower, summer type	No	Yes
Cauliflower, tropical type	No	No
Chinese broccoli	No	No
Collards	No	Yes
Kale	No	Yes
Kale, tropical type	No	No
Kohlrabi	No	Yes

Inflorescence and floral biology

The inflorescence of cole crops is racemose type, except cauliflower having cymose type, being more dwarf and umbrella shape may attain a length of 1-2 m. Flowers are borne on the main stem and its branches whose slender pedicels are only 1.5-2.0 cm long. The flowers are typically cruciferous, having four sepals, four petals, six stamens (two are short) and two carpels along with superior ovary, septum and two rows of campylotropous ovules (Figure 1). The sepals are green and erect. The petals are arranged perpendicular to each other, forming a cross i.e. cruciferous. Generally, the colour of petals may be light yellow, yellow, dark yellow or some time white. The bright yellow petals become 15-25 mm long and about 10 mm wide. The androecium is tetradynamous i.e. there are two short and four long stamens. The two functional nectaries are present which are situated between the bases of ovary and short stamens and the other two inactive nectaries at the bases of pairs of long stamens. Honey bees are the usual pollinating agents, though bumble bees and other syrphid flies may also be responsible for pollination. 

References

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Development of hybrids and hybrid seed production of onion

Gupta A and Singh BK. 2016. Development of hybrids and hybrid seed production of onion. In: Principles and Production Techniques of Hybrid Seeds in Vegetables (Singh B, Pandey S, Singh N, Manimurugan C, Devi J and Singh PM Eds). Training Manual No.  67, ICAR-IIVR, Varanasi, UP, pp 101-111.

Onion (Allium cepa L.) is a high value spice-cum-vegetable crop cultivated in almost all parts of the country for its tunicated bulbs. In India, onion occupies an area of 1.20 mha with the production of 19.42 mt. Globally, India ranks first in area and second in production of onion, but its productivity is low (16.1 t/ha) as compareto world’s productivity (19.3 t/ha) (Anonymous 2015). One option to achieve a quantum jump in yield and productivity is through harnessing the potential of heterotic vigour present among genetic resources. Heterosis breeding provides the opportunities for improvement in productivity; earliness; uniformity for maturity, and colour, shape and size of bulbs; and yield attributing characters. Most of the area under onion cultivation in India is covered by open pollinated varieties (OPVs) whereas the areas under hybrids have been increased significantly in developed countries. Now-a-days, both private and public sectors in India are paying more attention towards development of F₁ hybrids. Onion is a classical crop for exploitation of heterosis or hybrid vigour. Being a cross-pollinated crop, it exhibits wide variability in terms of maturity, bulb shape and size, bulb colour, day length requirement for bulbing, vernalization for flowering, TSS, drymatter content, etc. Hybrid seed production by hand emasculation and pollination can onlybe academic reality; commercially it is neither feasible nor economical. After the discovery of cytoplasmic genic male sterility (CGMS) by Jones and Clarke (1925), the phenomenon of heterosis breeding in onion is being exploited all over the world in long day as well as short day onions.

Use of male sterility in onion

The most important qualitative genes in onion are those that cause male sterility. In male sterile plants pollen fails to develop and they are therefore incapable of self-pollination. Hence, any seed produced result from only cross-pollination. This property has been utilized to produce F₁ hybrids which show hybrid vigour for various traits of economic importance. In the absence of male sterility, controlled cross-pollination without any self-pollination can be achieved by the laborious method of removing anthers from a flower head before they shed pollens followed by hand pollination with desired pollens. Such a procedure is too labour intensive, time consuming which is useful only for experimental breeding purpose.

Male sterility in onion was first exploited by Jones and Clarke using a male sterile genetic stock of cultivar ‘Italian Red’ found in breeding plots at Davis, California in 1925.  Fortunately, when this plant was prevented from being cross-pollinated, bulbils were produced in the flower head and it could be propagated. Jones and Clarke (1943) published this classical work describing the genetics of male sterility and indicating how it could be used to produce hybrid cultivars. On the basis of these techniques male sterility has since been exploited in more than 150 crop species (Kale and Munjal 2005). CGMS system presently used worldwide in onion for commercial exploitation of heterosis was originally derived from a variety ‘Italian Red 13-53’. The second source of CMS (T-cytoplasm) was discovered in a French cultivar ‘Jaunepaille des Venus’. This CMS line was found to be different than that from ‘Italian Red 13-53’ as three independent segregating restorer loci were identified in this line, responsible for its complex inheritance. It has common occurrence of restorers which makes this T-cytoplasm more difficult to use. Later on male sterility has been observed in several other onion populations, mainly in long-day cultivars e.g. Pukekohe Longkeeper, Red Wethersfield, Scott County Globe, Stuttgarter Riesen and Zittauer Glebe. In India, male sterility was identified in a local cultivar Nasik White Globe at IIHR, Bangalore (Pathak et al. 1980). The tapetal abnormalities and histochemical changes were mainly responsible for male sterility in onion and there was no role of meiotic abnormalities (Saraswathi and Veere Gowda 2006).

Snap bean (Phaseolus vulgaris L.): advances in genetic improvement

Singh BK, Lal H, Ranjan JK and Singh B. 2016. Snap bean (Phaseolus vulgaris L.): advances in genetic improvement. In: National Symposium on Vegetable Legumes for Soil and Human Health (Singh B, Singh M, Rai AB, Singh PM, Prasad RN, Mishra GP, Singh BK, Ranjan JK, Devi J, Seth T, Nagendran K., Chaukhande P, Kumar R, Gautam KK, Gujjar RS and Kumar YB Eds). ICAR-IIVR, Varanasi, 12-14 February 2016, pp 125-136.

Common bean (Phaseolus vulgaris L.), an important legume, is a rich source of protein, vitamins, minerals and fibre. The main categories of common beans, on the basis of uses, are dry beans (seeds harvested at complete maturity), snap beans (tender pods with reduced fibre harvested before the seed development phase) and shell beans (seeds harvested at physiological maturity) and. Snap bean is also known as French bean, garden bean, green bean, edible podded bean, string bean, fresh bean or vegetable bean. As the name implies, snap beans break easily when the pod is bent, giving off a distinct audible snap sound. The pods of snap beans (green, yellow and purple in colour) are harvested when they are rapidly growing, fleshy, tender (not tough and stringy), bright in colour, and the seeds are small and underdeveloped (8 to 10 days after flowering). After that period, excessive seed development reduces quality and the pod becomes fibrous, pithy and tough, and loses its bright colour. Snap bean seeds may also be used in dry static like the dry bean types. In that case pinto, kidney, pink, small red, etc. terms are used. In India, the dry bean type varieties are known as rajmash/rajmah, and snap bean named as rajmah phali in Hindi. Common beans display a wide range of growth habits from bush determinate to pole indeterminate types. Bush types are the most widely grown and are a relatively short duration crop; but on the other hand, in smallholder agriculture or in kitchen garden where land is scarce, labour-intensive high-yielding climbing beans getting popularity now-a-days. Dry bean is the largest pulse crop in the world with 23.60 mt of annual production grown on 29.29 mha area; and the top ten producing countries are Mayanmar (3.90 mt), India (3.63 mt), Brazil (2.79 mt), China (1.46 mt), USA (1.45 mt), Tanzania (1.20 mt), Mexico (1.08 mt), Kenya (0.61 mt), Ethiopia (0.46 mt) and Rawanda (0.43 mt). Moreover, snap beans’ global annual production and area is about 20.74 mt and 1.54 mha, respectively with maximum production in China (16.20 mt) followed by Indonesia (0.87 mt), India (0.62 mt), Turkey (0.61 mt), Thailand (0.31 mt), Egypt (0.25 mt), Spain (0.17 mt), Italy (0.14 mt), Morocco (0.13 mt) and Bangladesh (0.09 mt) [FAOSTAT 2012]. In India, it is grown on an area of about 1 lakh ha mainly in the states of Maharashtra, Jammu and Kashmir, Himachal Pradesh, Uttarakhand, North-East hills, Nilgiri (Tamil Nadu), hills of central India, Palni hills (Kerala) Chickmagalur (Karnataka) and Darjeeling hills (West Bengal). The tender pods of snap bean are good source of ascorbic acid (vitamin C), phylloquinone (vitamin K), β-carotene (vitamin A), riboflavin (vitamin B2), niacin (vitamin B3), Mn, K, Ca, P, Fe and omega-3 fatty acid. It is a legume crop, do fix some nitrogen but the N fixing bacteria are not active as with other legumes; therefore there is need to fertilize the field with nitrogenous fertilizer to harness the yield potential.

Origin and Domestication

The genus Phaseolus is originated in the American continent and a large number of its species is found in Mesoamerica (Freytag and Debouck 2002; Acosta-Gallegos et al. 2007). Moreover, common bean has originated in southern Mexico to Central America (Mesoamerica), while Ecuador-Peru-Bolivia region is the secondary centre of origin (Gepts 1998; Bellucci et al. 2014). The hypothesis of Mesoamerican origin of the common bean is supported by the observations that the closest relatives of wild P. vulgaris are distributed throughout Mesoamerica (Schmit et al. 1993; Delgado-Salinas et al. 2006). The genus Phaseolus comprised of about 70 species and has contributed to human welfare with five cultigens domesticated in pre-Columbian times: common bean (P. vulgaris L.), year bean (P. dumosus Macfad.), runner bean (P. coccineus L.), tepary bean (P. acutifolius A Gray) and lima bean (P. lunatus L.). Among the five domesticated species, P. vulgaris is the most important economically that accounts for more than 90% of the cultivated Phaseolus worldwide (Singh 2001; Acosta-Gallegos et al. 2007). The current distribution of the wild common bean encompasses a large geographical area: from northern Mexico to north-western Argentina. Prior to domestication, wild P. vulgaris had diverged into two major gene pools on the basis of geographic distribution: (i) the Mesoamerican i.e. Middle America and (ii) the Andean i.e. Andean South America which can be distinguished at the morphological, biochemical and molecular levels (Singh et al. 1991a), and also display partial reproductive isolation caused by F₁ lethality (Gepts and Bliss 1985). With the exceptions, no successful recombination has occurred between the two major gene pools. A first exception is provided by Chilean landraces which showed signs of introgession from the Mesoamerican gene pool based on phaseolin seed protein and allozymes (Paredes and Gepts 1995). The second exception is evolution of snap bean cultivars. Although they originated in the Andean gene pool, many varieties are actually intermediate between the two gene pools as evidenced by RAPD markers (Skroch and Nienhuis 1995). This intermediate position may be attributed to recent breeding efforts aimed at introducing disease resistance from the Mesoamerican gene pool into the snap bean cultivars (Gepts 1998). While only these two major gene pools are recognized in the domesticated population, the geographical structure of the wild form of the common bean is more complex, with an additional third gene pool that is localized between Peru and Ecuador, and characterized by a specific storage seed protein, phaseolin type I (Debouck et al. 1993; Kami et al. 1995). Generally, the Mesoamerican gene pool possesses higher content of lectin, Ca, P, S and Zn than the Andean gene pool but lower phaseolin and Fe (Islam et al. 2002). Further, the two major gene pools in P. vulgaris have been divided into six races (Mesoamerican gene pool: Mesoamerica, Durango and Jalisco; and Andean gene pool: Nueva Granada, Peru and Chile) as the members of each race share distinct morphological, agronomic, physiological and biochemical traits; and differ from other races in allelic frequencies of genes controlling these traits (Singh et al. 1991a).

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VRKALE-1: a tropical kale, first of its kind in the world

VRKALE-1: a tropical kale, first of its kind in the world

BK Singh*, Bijendra Singh and PM Singh

ICAR-Indian Institute of Vegetable Research (ICAR-IIVR), Shahanshahpur-221305, Varanasi, UP, India

*E-mail: bksinghkushinagar@yahoo.co.in

Genetic Resources and Crop Evolution, 2017, 64(2): 437-440, DOI: 10.1007/s10722-016-0477-x

Abstract

Kale (Brassica oleracea L. var. virdis L.), a very versatile leafy vegetable, is typically a temperate cole crop and is an excellent source of health benefiting phyto-nutrients. A unique tropical kale genotype, first of its kind in the world, has been identified at ICAR-Indian Institute of Vegetable Research, Varanasi, Uttar Pradesh, India. Christened as ‘VRKALE-1’, it bolts and flowers under North Indian plain conditions (11.8-23.5 °C temperature) and doesn’t require vernalization (low temperature <7 °C for 6-8 weeks). This is a smooth leafed kale (subvar. plana Peterm.) having soft, young, tender and crispy leaves, measuring 22-30 cm in length, are ready for first picking in 23-28 days after transplanting and thereafter at weekly interval. A single plant produces 100-125 leaves in 9-12 pickings weighing 1.5-1.8 kg leaf biomass and the leaf yield potential is very high (55-60 t/ha). It bears flowering stalk after 110-120 days of transplanting, having racemose type of inflorescence. Like tropical cauliflower which evolved in India; it is expected that tropical kale will certainly play a pivotal role in expanding the adoption, popularity and genetic base of kale in future, particularly in hitherto unexploited areas.

Key words: Brassica oleracea var. virdis; Kale; Tropical cole crops; Nutrient; Vernalization.