(a) What are the diagnostic characters of the families – Cucurbitaceae and Poaceae ? Write the botanical names and economic…

(a) Diagnostic Characters and Economic Importance of Cucurbitaceae and Poaceae

Cucurbitaceae are mostly climbing or trailing annual herbs, climbing by spirally coiled tendrils (at the side of the petiole), with stems and leaves often rough with stiff hairs. Leaves are alternate, simple, palmately lobed and veined, and often cordate at the base. Flowers are unisexual, usually monoecious (dioecious in Coccinia and Trichosanthes dioica), pentamerous, with a campanulate calyx and a gamopetalous corolla. The androecium has 5 stamens that usually appear as 3 (two pairs fused and one free, 2+2+1), with sinuous (S- or U-shaped) anther lobes; in Cucurbita the anthers cohere into a central column. The ovary is inferior, tricarpellary and syncarpous, unilocular with three intruding parietal placentae, so that it often appears trilocular, and bears many ovules. The fruit is a pepo, a berry with a hard rind.

Five economically important members:

1. Cucumis sativus (cucumber): fruits eaten raw as salad and pickled.
2. Citrullus lanatus (watermelon): dessert fruit; the seeds are also eaten.
3. Cucurbita pepo / C. maxima (pumpkin): fruits as a vegetable; seeds yield edible oil.
4. Luffa aegyptiaca (sponge gourd): young fruits as a vegetable; the fibrous vascular network of mature fruit is used as a bath sponge and filter.
5. Momordica charantia (bitter gourd): fruits as a vegetable, and in traditional medicine for diabetes. Lagenaria siceraria (bottle gourd) and Cucumis melo (muskmelon) are other valid examples.

Poaceae (Gramineae) are annual or perennial herbs (woody in bamboos) with a cylindrical culm that has solid nodes and usually hollow internodes. Leaves are alternate and distichous, each with a split (open) sheath, a ligule at the junction of sheath and blade, and a linear blade with parallel venation. The unit of inflorescence is the spikelet, borne in spikes, racemes or panicles; each spikelet has two sterile glumes at the base and florets each enclosed by a lemma and a palea. The perianth is reduced to 2–3 lodicules. Stamens are usually 3 (6 in rice and bamboos), with versatile anthers on long filaments (wind pollination). The ovary is superior and unilocular with one basal ovule, and usually bears two feathery stigmas. The fruit is a caryopsis, with the pericarp fused to the seed coat.

Five economically important members:

1. Oryza sativa (rice): staple cereal; straw as fodder; rice bran oil.
2. Triticum aestivum (wheat): cereal for flour (atta, maida) and semolina.
3. Zea mays (maize): food, poultry and cattle feed, starch and ethanol.
4. Saccharum officinarum (sugarcane): sugar, jaggery; molasses for ethanol; bagasse for paper and fuel.
5. Bambusa / Dendrocalamus spp. (bamboo): construction, paper pulp, handicrafts; young shoots are eaten. Cynodon dactylon (doob grass: lawns, fodder) and Pennisetum glaucum (pearl millet) are other valid examples.

(b) Vavilov's Contributions; Dye-Yielding Plants of India

N.I. Vavilov (1887–1943), who led plant-collecting expeditions to over 60 countries from the Institute of Plant Industry at Leningrad, made the following contributions:

1. Centres of origin: he proposed that each crop originated where its greatest genetic diversity is found today, and identified eight main centres (1935): Chinese, Hindustan (Indian), Central Asiatic, Near Eastern, Mediterranean, Abyssinian, South Mexican–Central American, and South American, with the Indo-Malayan sub-centre attached to the Hindustan centre.
2. Differential phytogeographic method: a crop's centre is located by mapping the region of maximum varietal diversity, where dominant alleles and endemic forms are concentrated; recessive forms accumulate towards the periphery.
3. Primary and secondary centres: he distinguished the original home of a crop from regions where it later diversified.
4. Law of Homologous Series in Variation (1920): related species and genera show parallel series of variation, so a variant found in one species can be predicted and searched for in its relatives.
5. Germplasm collection: his institute built one of the first great seed collections, the forerunner of modern gene banks such as India's National Gene Bank at ICAR-NBPGR, New Delhi.

He placed rice, sugarcane, chickpea, pigeon pea, brinjal, cucumber, mango, many Citrus species and diploid cotton (Gossypium arboreum) in the Hindustan centre.

Three dye-yielding plants of India:

1. Indigofera tinctoria (indigo): leaves, fermented to give the blue dye indigo.
2. Rubia cordifolia (Indian madder, manjistha): roots, which give a red dye.
3. Lawsonia inermis (henna, mehndi): leaves, which give an orange-red dye for skin, hair and textiles. Crocus sativus (saffron, dried stigmas), Bixa orellana (annatto, seed coat) and Butea monosperma (flame of the forest, flowers) are also acceptable.

(c) Pollen Storage and Test-Tube Fertilization

Importance of pollen storage: it allows crosses between parents that flower at different times or in different places; it enables pollen to be exchanged between breeding stations and countries more easily than whole plants; it provides a steady supply of pollen for hybrid seed production and for fruit set in crops like date palm; it conserves the male germplasm of rare and endangered species, complementing seed banks; and it supports studies of pollen physiology, allergy and haploid breeding.

Methods of storage: pollen longevity depends mainly on temperature, humidity and oxygen.

1. Low temperature and controlled humidity: storage at 0–5°C, or at −18 to −20°C in a deep freezer, after drying to a low moisture content (often 5–10%). Grass pollen (three-celled, short-lived) needs more care than two-celled pollen.
2. Cryopreservation: dried pollen is stored in liquid nitrogen (−196°C), where metabolism stops and viability lasts for years.
3. Freeze-drying (lyophilisation) and vacuum drying: pollen is dehydrated under vacuum and sealed, sometimes under an inert gas.
4. Storage in organic solvents such as hexane, benzene or acetone for some species. Before use, stored pollen is checked for viability by staining (e.g., the fluorochromatic reaction test) or by in vitro germination.

**Test-tube (in vitro) fertilization: in this technique, excised ovules (ovular pollination) or whole placentae with ovules attached (placental pollination) are cultured aseptically on a nutrient medium and dusted directly with pollen. The pollen tubes enter the ovules without passing through the stigma and style, so pre-fertilization barriers that act there, such as self-incompatibility and interspecific incompatibility, are bypassed. The ovules then develop into seeds in culture. Kanta, Rangaswamy and Maheshwari (1962)** first achieved it in Papaver somniferum at the University of Delhi; it was later used for Nicotiana and Melandrium crosses (Zenkteler) and to obtain hybrids that fail on normal pollination. It also helps the study of fertilization physiology.