Dalbir Singh

The reliable and rapid polymerase chain reaction (PCR) diagnosis for Xanthomonas axonopodis pv. punicae in pomegranate

Bacterial blight is a major disease in pomegranate (Punica granatum) cultivation in India threatening the export potential of this important fruit crop. The disease is caused by a yellow pigmented, Gram negative, rod shaped bacterium, Xanthomonas axonopodis pv. punicae. We developed a polymerase chain reaction (PCR) based detection technique for this blight pathogen using primers designed from gyrB gene. A primer set KKM5 and KKM6 was synthesized based on sequence alignment of 530 nucleotides of C-terminus region in the gyrB genes from 15 different bacterial strains. The primer set was validated for amplification of 491 bp of gyrB gene. No amplification was observed in other phytopathogenic Xanthomonads including Xanthomonas axonopodis pv. citri, Xanthomonas axonopodis pv. phaseoli, Xanthomonas axonopodis pv. mangiferaeindicae, Xanthomonas campestris pv. manihotis, Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicola, Xanthomonas axonopodis pv. axonopodis and Pantoea agglomerans. The developed technique could detect the pathogen in infected pomegranate plant samples including leaf, fruit and stem within 3 h, at a detection limit 0.1 ng µl -1 template DNA.

Transmission of seed-borne inoculum ofMacrophomina phaseolina from seed to plant

Macrophomina phaseolina is a serious pathogen which is externally as well as internally seed-borne. It causes failure of seed germination and browning and rotting of seedlings. The presence of pathogen in infected and healthy looking seedlings was tested by clearing, sectioning and incubation techniques. After 8 weeks almost every surviving plant developed pale yellow to brown circular or oval concentric spots on leaves, stem and capsules. Mycelium and microsclerotia were observed in the peripheral region of the lesions. Splitted root, stem and capsule also showed the presence of microsclerotia. Cleared wholemounts of leaf and stem and T.S. and L.S. of stem showed inter- and intracellular mycelium in cortex, xylem and pith cells. Microsclerotia were also observed. In capsule, infection was recorded on its inner wall, septum, placenta and seeds spreading from base to apex.

Development and structure of seed inTacsonia Juss. andPassiflora L.

Tricarpellary, syncarpous, unilocular ovary bears horizontal, bitegmic, crassinucellate and antropous ovules on three parietal placentae. Micropyle iszig-zag formed by both the integuments. The embryo sac is of Polygonum type and the pollen tube is persistent. The development of endosperm is nuclear and at maturity it becomes ruminate. The mature embryo is spatulate with two thin cotyledons and a short stubby hypocotyledonary region.The outer integument is 4-layered inTacsonia and 3-layered inPassiflora but the inner is 3-layered in both. Seeds are covered with a succulent coloured aril which originates as a small outgrowth round the funiculus at the organised embryo sac stage. The seed coat is formed by both the integuments and is 7- or 8-layered inT. mollissima and 6-layered inP. caerulea andP. edulis. It comprises 6 zones of which the seed epidermis, radially elongated inner epidermis of the outer integument, the main sclerotic layer formed by outer epidermis of the inner integument are most conspicuous. The sclerotic layer consists of macrosclereids of various sizes and together with inner epidermis of the outer integument forms the ingrowths which make the endosperm ruminate.

Embryological studies on Indian Taraxacum Weber. Embryo sac, endosperm and embryo

Abstract The present paper deals with the embryological studies of ten species of Taraxacum, out of which nine polyploid species are apomictic and one diploid species T. wallichii shows normal sexual behaviour. Occasional formation of normal megaspore tetrads and triads are observed in tetraploid and triploid species. Autonomous development of endosperm from the secondary nucleus seems to be the rule. The growth of endosperm is relatively slow.

Cytological studies in the genusTaraxacum weber

The Karyotype of seven species are described. Three of them are tetraploid (2n=32) and four triploid (2n=24). The chromosome numbers ofT. banhyhalense, T. tenebristylum, T. harbhajan-singhii ssp.pahalgamense, T. flavum andT. vulpinum f.pallidocarpum are recorded for the first time. Chromosomes are mostly medium to short in size. On the basis of chromosome morphology, in all sixteen chromosome types are recognised. None of these species shows multiple identical chromosome sets. The role of chromosome size and the number of chromosome pairs in multiple sets in evolution has been discussed.

Morphology and embryology ofMarah macrocarpa Greene

The ovary is usually tricarpellary, rarely bicarpellary and covered with spines and glandular and eglandular hairs inMarah macrocarpa Greene. Structure and development of spines and two types of hairs are described. Ovules are anatropous, bitegmic and crassinucellate. The ovular bundle ramifies after fertilization. Development of embryosac is of Polygonum type. The pollen-tube is persistent and sometimes dilates at the base of the nucellar beak. The endosperm is Nuclear and enucleate cytoplasmic nodules are formed. The wall formation is progressive and chalazal endosperm haustorium is short and coenocytic. Rarely, it is rudimentary. Embroyogeny is suggestive of Onagrad type. Hemitriand hemitetracotyledonary embryos are also recorded.The seedcoat develops from the outer integument alone. The mature seedcoat comprises seed epidermis, hypodermis, main sclerenchymatous layer of narrow osteosclereids, (all derived from the outer epidermis of outer integument) aerenchyma and chlorenchyma.

Structure and development of seedcoat in Cucurbitaceae

The paper describes the development and structure of seedcoat inBiswarea tonglensis, Edgaria darjeelingensis, andHerpetospermum pedunculosum. The ovules are anatropous, bitegminal, and crassinucellar; they are horizontally disposed inBiswarea but pendulously inEdgaria andHerpetospermum. The ovular supply is unbranched inBiswarea andHerp etosperumum but ramifies in the lower part of seed inEdgaria. The outer integument alone forms the seedcoat which, at maturity, is differentiated into five zones. The epidermis is heterogeneous consisting of upright cells in all these plants. The hypodermis is sinuate, cells thick-walled and lignified; it is 10 to 14-layered in furrows and 20 or more-layered in ridges inBiswarea, 5 or 6-layered in furrows and 8 to 12-layered in ridges inEdgaria, and 2 or 3-layered in furrows and up to 10-layered in ridges inHerpetospermum. The main sclerenchymatous layer consists of osteosclereids. The seedcoat in all these plants is built on a common pattern and suggests a close relationship among them. A key is proposed to distinguishBiswarea, Edgaria andHerpetospermum from each other using external and internal characters of their seeds.