Infection of potato tubers with soft rot bacteria

Stolons attached to developing potato tubers were inoculated with the soft rot bacterium Erwinia carotovora var. atroseptica. Almost all the stolons rotted, but soft rots developed in less than 10% of new tubers; the bacterium was isolated later from these tubers. No rots developed in the other tubers but the bacterium was later isolated from about half of them. It could not be isolated from tubers attached to inoculated stolons where the rot on them did not extend to the tuber or from tubers attached to stolons that were not inoculated though many of these rotted. The bacterium was reisolated from almost all arrested lesions in tubers inoculated 8 month earlier with E. carotovora var. atroseptica. Blackleg did not develop from plants grown fom these tubers under various soil conditions. It did develop in a large proportion of plants from tubers inoculated shortly before planting and grown in cool, wet soil. Less than 1% blackleg developed in plants grown from tubers from plants with blackleg or from plants immediately adjacent. The presence of pectolytic bacteria and E. caratovora var. atroseptica in seed and new tubers was investigated during June, July and August. Although E. caratovora var. atroseptica was obtained from c. 40% tubers, only c. 0·3% of c. 8400 plants developed blackleg. The bacterium was isolated from only three of 160 new tubers sampled during the summer.     

Stem canker (Rhizoctonia solani) of maincrop potatoes.

In two years, potato plants were sampled at 1- or 2- weekly intervals from plots planted with seed tubers bearing sclerotia of Rhizoctonia solani (black scurf) and with seed without sclerotia either infested or not with cultures of R. solani at planting. Sprouted King Edward seed was used in 1981 and sprouted and non-sprouted King Edward and Pentland Crown seed in 1982. In both years 60–80% of shoots from seed with sclerotia and 90% of shoots from seed inoculated at planting were affected with stem canker. Most disease developed before shoots emerged although it gradually increased later when new shoots arising both from seed tubers or as branches on shoots with damaged apices (pruned shoots) became infected before they emerged. Sprouting seed tubers bearing sclerotia decreased the disease on both cultivars but with soil-applied inoculum the disease was more severe on plants from sprouted than non-sprouted seed. Some stolons were infected by R. solani soon after they developed and incidence of infection later increased. Thirty to 50% of stolons were infected on plants from infected seed tubers and 60% on plants with soil-applied inoculum. With both cultivars and sources of inoculum about 70% of the infected stolons had their apices killed (pruned).     

Musa nagalandiana sp. nov. (Musaceae) from Nagaland,northeast India

Musa nagalandiana S. Dey & Gogoi, a new species of Musa sect. Musa, is described and illustrated from Zunheboto district, Nagaland, India based on morphological characteristics observed in the field. The new species is rare in the wild and found in tropical semi‐evergreen forest on the bank of the river Doyang, in Zunheboto district of Nagaland. A key to M. nagalandiana and related taxa is provided.     

Stem canker (Rhizoctonia solani) on five early and seven maincrop potato cultivars I. Infection of shoots, stolons and tubers

In 1983 and 1984, potato seed tubers of five early and seven maincrop cultivars were inoculated with cultures of Rhizoctonia soluni during planting to simulate severe seed infection. Shoot and stolon infection was assessed in June-August and black scurf on tubers recorded after harvest in October. Almost all shoots of all cultivars had stem canker in both years and disease on shoots, stolons and tubers was more severe in 1984 than in 1983. In 1983 similar amounts of disease developed on all early cultivars and between 11% (Ulster Sceptre) and 32% (Maris Peer) shoots were pruned off. Maris Peer had a stem canker score lower than other cultivars in 1984 but more than half the shoots were pruned off. Shoot pruning on Estima, Ulster Prince and Ulster Sceptre was more common on plants from sprouted than non-sprouted seed. Between 30 and 50% of stolons were pruned off. After harvest in 1985, black scurf was least prevalent on Arran Comet and Maris Peer tubers and in 1984 on Arran Comet and Estima tubers from non-sprouted seed. Of the maincrop cultivars, King Edward plants from sprouted seed had many shoots pruned off in both years. Shoot pruning was also prevalent on Maris Piper and Pentland Squire plants from non-sprouted seed. Record had fewest pruned shoots and stolons and the lowest stem canker score. The disease was more severe on Pentland Crown and Maris Piper plants from non-sprouted than sprouted seed. Black scurf was most common on Cara and King Edward tubers in 1983 and on King Edward and Record tubers in 1984. In both years few shoots but many tubers were infected on plants from non-inoculated seed and the significance of this is discussed.     

Occurrence of jasmonic acid in organs of Solanum tuberosum L. and its effect on tuberization

The aims of this study were to demonstrate the endogenous presence of jasmonic acid (JA) in roots, stolons and periderm of new formed tubers, by means of bioassays, ELISA and GC-MS, and to test a microdrop bioassay using the leaflets of potato cuttings cultured in vitro. Our results confirm the existence of JA by bioassays and GC-MS in foliage, stolons, roots and tuber periderm.Abbreviations DW dry weight - GC-MS gas chromatography-mass spectrometry - JA jasmonic acid - MeOH methanol - SD short day     

Piper relictum sp. nov. (Piperaceae) from northern Western Ghats,India

A new species of Piper, P. relictum Lekhak, S. S. Kambale & S. R. Yadav sp. nov. is described and illustrated. It grows as a climber on the edges of high altitude lateritic plateaus in evergreen forests of the northern Western Ghats in India. The new species is similar to P. galeatum, but differs in the characters of the male inflorescence.     

Eleocharis khandwaensis sp. nov. (Cyperaceae) from the Madhya Pradesh,India

A new species, Eleocharis khandwaensis Mujaffar, Chandore & S. R. Yadav is described from the Bamangaon village of Khandwa district in Madhya Pradesh state, India. This species belongs to Eleocharis subgen. Limnochloa (P. Beauv. ex Lestib.) Torr. and it is similar to E. lankana T. Koyama but differs in having stolons, weak bristles spinules of perianth, achenes with annulate apex with a short neck, truncate achene base, dark brown to black coloured achenes and nut surface epidermal cells that are isodiametrically hexagonal to pentagonal. Eleocharis khandwaensis grows in ponds along road sides in the Bamangaon and Tirandaz villages.     

Effects of Temperature on Bud-Sprouting and Early Growth of Cyperus esculentus in the Dark

Cyperus esculentus tubers and early growth of their sprouts. Percent sprouting increased with increasing temperature within the range of 12 to 38 C, while no sprouting occurred at 10 C and few tubers sprouted at 42 C. The rate of sprouting also increased with temperature up to 35 C. A base temperature of 11.4 C was determined for bud-sprouting of tubers in this species. Higher temperatures led to larger sprouts and greater survival rate. In particular, increased temperature favored root growth, and hence resulted in high root: shoot ratio of the sprouts. Larger tubers produced larger sprouts as a consequence of mobilizing a greater amount of their reserves, but they tended to utilize a smaller proportion of their reserves. The efficiency of reserve utilization significantly differed among the incubation temperatures, and its relation with temperature followed a quadratic pattern. This pattern is different from that documented for the bud-sprouting of rhizomes and stolons of other perennials. Our results demonstrate that temperature is crucial to the successful establishment of C. esculentus. Received 24 June 1999/ Accepted in revised form 14 December 1999     

Paleoequatorial rain forest of western India during the EECO: evidence from Uvaria L. fossil and its geological distribution pattern

During the early Eocene, Rajasthan was positioned near the equator and had a warm and humid tropical climate dominated by tropical rainforests like the present-day equatorial forests of South India. Many of the plants retrieved as fossils from Rajasthan are growing there as refugee. This study further strengthens this view as it reports a new species of Uvaria L. from the early Eocene sediments of Bikaner (Rajasthan) showing its best resemblance with the extant U. zeylanica Deless. ex DC., which is presently growing in the evergreen forests of South India and Sri Lanka. The genus is thought to have originated in Africa, and the present finding gives an idea about its geologic distribution in Asia and Australasia via India relying on ‘stepping stone’ hypothesis during the Early Eocene Climatic Optimum (EECO) when climatic conditions were favourable for the luxuriant growth of tropical vegetation. A general cooling trend after EECO and change in the configuration of land and sea affected the climate on the regional scale causing total devastation of tropical evergreen forests that existed in western India during the depositional time; this change is ultimately responsible for creating dry and desertic conditions prevailing in the area at present.     

Cell division and cell enlargement during potato tuber formation

Cell division and cell enlargement were studied to reveal the developmental mechanism of potato tuberization using both in vivo in vitro culture systems. Distribution of cells in S-phase was visualized by immunolabelling of incorporated bromodeoxyuridine (BrdU). Mitosis was detected in DAPI (4,6-di-amidino-2-phenylindole) or toluidine blue-stained sections. Timing and frequency of cell division were determined by daily cell counting, and cell enlargement was deduced from measurements of cell diameters.Under in vivo conditions, lateral underground buds developed into stolons due to transverse cell divisions and cell elongation in the apical region of the buds. At the onset of tuber formation, the elongation of stolons stopped and cells in pith and cortex enlarged and divided longitudinally, resulting in the swelling of the stolon tip. When tubers had a diameter of 0.8 cm, longitudinal divisions had stopped but randomly oriented division and cell enlargement occurred in the perimedullary region and continued until tubers reached their final diameter.In vitro tubers were formed by axillary buds on single node cuttings cultured under tuber-including conditions. They stopped growing at a diameter of 0.8 cm. Pith and cortex were involved in tuberization such as that found during the early stage of in vivo tuberization (<0.8 cm in diameter). The larger size of in vivo tubers is, however, due to further development of the perimedullary region, which is lacking in vitro conditions.Keywords: Cell division, cell enlargement, DNA synthesis, in vitro culture, potato, tuber formation.      

Developmental processes of achlorophyllous orchid, <Emphasis Type="Italic">Epipogium roseum</Emphasis>: from seed germination to flowering under symbiotic cultivation with mycorrhizal fungus

We have achieved the symbiotic cultivation of an apparently achlorophyllous orchid, Epipogium roseum Lindl., with a mycorrhizal fungus isolated from an underground organ of this orchid. Although the seed germination rate was extremely low, subsequent growth from protocorm to flowering was induced in a medium containing volcanic soils and sawdust. Stolons elongated from each protocorm, and rhizomes were formed at certain intervals on the stolons. Some of the rhizomes developed into a coralloid form, and tubers were formed from the coralloid rhizomes. The coralloid rhizomes degenerated concurrently with maturation of the tubers. Six months after seed sowing, around 80 tubers were produced from a single protocorm. An inflorescence appeared from each of the large tubers, and the process to flowering was observed in one of these. Consequently, the developmental processes from seed to flowering in E. roseum was clearly revealed in this study.     

Expression of a chimaeric granule-bound starch synthase-GUS gene in transgenic potato plants

Granule-bound starch synthase is the key enzyme in amylose synthesis. The regulation of this gene was investigated using a chimaeric gene consisting of a 0.8 kb 5 upstream sequence of the granule-bound starch synthase gene from potato and the -glucuronidase gene which was introduced into potato using an Agrobacterium tumefaciens binary vector system. The chimaeric gene was highly expressed in stolons and tubers, whereas the expression in leaves, stems or roots from greenhouse-grown plants was relatively low. However, leaves from in vitro grown plantlets exhibited an elevated GUS expression. The expression of the chimaeric gene was inducible in leaves by growth on relatively high concentrations of sucrose, fructose and glucose and was about 30- to 50-fold higher than in leaves from greenhouse-grown plants. The granule-bound starch synthase gene is expressed organ-specifically since stolons and tubers showed GUS activities 125- to 3350-fold higher than in leaves. The activities in these two organs are 3- to 25-fold higher than the expression of the CaMV-GUS gene. Histochemical analysis of different tissues showed that only certain regions of leaves and roots express high GUS activities. Stolons and tubers show high expression.     

Genomic and functional characterization of StCDPK1

StCDPK1 is a calcium dependent protein kinase expressed in tuberizing potato stolons and in sprouting tubers. StCDPK1 genomic sequence contains eight exons and seven introns, the gene structure is similar to Arabidopsis, rice and wheat CDPKs belonging to subgroup IIa. There is one copy of the gene per genome and it is located in the distal portion of chromosome 12. Western blot and immunolocalization assays (using confocal and transmission electron microscopy) performed with a specific antibody against StCDPK1 indicate that this kinase is mainly located in the plasma membrane of swelling stolons and sprouting tubers. Sucrose (4–8%) increased StCDPK1 protein content in non-induced stolons, however the amount detected in swelling stolons was higher. Transgenic lines with reduced expression of StCDPK1 (β7) did not differ from controls when cultured under multiplication conditions, but when grown under tuber inducing conditions some significant differences were observed: the β7 line tuberized earlier than controls without the addition of CCC (GA inhibitor), developed more tubers than wild type plants in the presence of hormones that promote tuberization in potato (ABA and BAP) and was more insensitive to GA action (stolons were significantly shorter than those of control plants). StCDPK1 expression was induced by GA, ABA and BAP. Our results suggest that StCDPK1 plays a role in GA-signalling and that this kinase could be a converging point for the inhibitory and promoting signals that influence the onset of potato tuberization.     

Morphology and growth of stolons and rhizomes in three clonal grasses,as affected by different light supply

In this paper, the hypothesis is tested that, in clonal grasses producing stolons and/or rhizomes, stolons always show a higher morphological plasticity than rhizomes in response to variation in light availability.Agrostis stolonifera (a stoloniferous grass),Holcus mollis (a rhizomatous grass) andCynodon dactylon (a grass forming both stolons and rhizomes), were grown in pots and subjected to three levels of light intensities. Both stolons and rhizomes branched more intensively under higher light levels. Irrespective of species, stolons consisted of longer internodes under lower light levels, while rhizome morphology did not respond significantly. Biomass partitioning to rhizomes was lower under lower light intensities while partitioning to stolons was not affected. Rhizomes usually had more dormant buds than did stolons. Our results suggest that stolons serve primarily as foraging organs for light, whereas the main function of rhizomes is storage of meristem and carbohydrates, irrespective of whether the grass species involved produces both rhizomes and stolons or only one type of spacer.     

SYMMETRY AND DEVELOPMENT OF LIMNOBIUM SPONGIA (HYDROCHARITACEAE)

Limnobium spongia produces upright vegetative axes and prostrate stolons. The upright axes bear new stolons, whereas the stolons bear new upright axes and fertile and sterile branching systems. Upright axes and fertile and sterile branching systems are all interpreted to have sympodial growth. However, it was not determined whether growth of stolons is monopodial or sympodial. Both stolons and upright axes branch in alternate plastochrons, and branching is achieved solely by the bifurcation of apical meristems. Each meristematic bifurcation is interpreted to represent the formation of a precocious lateral bud. The upright axes develop from presumed precocious lateral buds on stolons, whereas such buds on upright axes produce renewal shoots. Limnobium spongia exhibits a marked degree of mirror-image symmetry.     

Tuberization in Potato at High Temperatures: Gibberellin Content and Transport from Buds

Warm temperatures (35°C day/30°C night) which inhibittuberization in potato (Solanum tuberosum L., cv. Sebago) increasedgibberellin activity in crude extracts from buds, but not frommature leaves, as determined by the lettuce hypocotyl bioassay.Changes in the growth of tubers and stolons indicate the occurrenceof basipetal movement of GA₃ applied to the terminal bud ora mature leaf. ¹⁴C labelling from GA₃ or mevalonic acid injectedjust below the terminal bud was recovered in the lower shoot,stolons and tubers, but the amount transported was greater atcool temperatures (20/15°C). It is concluded that high temperaturespromote the synthesis of gibberellin in the buds rather thantransport to the stolons. Solanum tuberosum L., potato, tuberization, gibberellin     

Photosynthetic assimilation of 14C into amino acids in potato (Solanum tuberosum) and asparagine in the tubers

Asparagine is the predominant free amino acid in potato tubers and the present study aimed to establish whether it is imported from the leaves or synthesised in situ. Free amino acid concentrations are important quality determinants for potato tubers because they react with reducing sugars at high temperatures in the Maillard reaction. This reaction produces melanoidin pigments and a host of aroma and flavour volatiles, but if free asparagine participates in the final stages, it results in the production of acrylamide, an undesirable contaminant. ¹⁴CO₂ was supplied to a leaf or leaves of potato plants (cv. Saturna) in the light and radioactivity incorporated into amino acids was determined in the leaves, stems, stolons and tubers. Radioactivity was found in free amino acids, including asparagine, in all tissues, but the amount incorporated in asparagine transported to the tubers and stolons was much less than that in glutamate, glutamine, serine and alanine. The study showed that free asparagine does not play an important role in the transport of nitrogen from leaf to tuber in potato, and that the high concentrations of free asparagine that accumulate in potato tubers arise from synthesis in situ. This indicates that genetic interventions to reduce free asparagine concentration in potato tubers will have to target asparagine metabolism in the tuber.