红芽芋球茎片两步法离体快繁及其再生苗生理和光合特性研究

以江西铅山红芽芋(Colocasia esculenta L.Schott var.cormosus‘Hongyayu’)试管苗为材料,建立了芋球茎片两步法离体快繁体系,并对其再生苗的形态指标、染色体数目、生理和光合特性以及叶绿素荧光特性进行了检测。结果表明:(1)红芽芋球茎片单芽诱导的最佳培养基为MS+KT 2 mg/L+6-BA 1 mg/L+NAA0.1mg/L,诱导培养30d后将单芽从球茎片上分离,再接种到生根培养基(MS+KT 2mg/L+NAA 0.1mg/L)上培养30d即可形成完整植株,移栽成活率高达98%;(2)由球茎片单芽、丛生芽、不定芽离体快繁获得的红芽芋再生苗在形态指标、叶下表皮气孔参数、染色体数目、生理生化指标以及叶片光合特性参数和叶绿素荧光特性方面均无显著差异。说明红芽芋球茎片两步法离体培养的再生苗繁殖系数高、染色体数目稳定,该离体快繁体系可应用于江西铅山红芽芋的工厂化生产。     

Transmission of Tomato spotted wilt virus isolates able and unable to overcome tomato or pepper resistance by its vector Frankliniella occidentalis

Tomato spotted wilt virus (TSWV) causes serious diseases of many economically important crops. Disease control has been achieved by breeding tomato and pepper cultivars with the resistance genes Sw‐5 and Tsw, respectively. However, TSWV isolates overcoming these genetic resistances have appeared in several countries. To evaluate the risk of spread of these resistance‐breaking isolates, we tested their ability of transmission by the main vector of TSWV, the thrips Frankliniella occidentalis. We compared the transmission rate by thrips of six TSWV isolates of different biotype (able or unable to overcome this resistance in pepper and tomato), and with divergent genotype (A and B). Our results indicate that the transmission rate was related to the amount of virus accumulated in thrips but not to virus accumulation in the source plants on which thrips acquired the virus. No correlation was found between transmission efficiency by thrips and the genotype or between transmission efficiency and the ability of overcoming both resistances. This result suggests that resistance‐breaking isolates have the same potential to be transmitted as the isolates unable to infect resistant tomato and pepper cultivars.     

Fruit and seed heteromorphism in the cold desert annual ephemeral Diptychocarpus strictus (Brassicaceae) and possible adaptive significance

Background and Aims

Diptychocarpus strictus is an annual ephemeral in the cold desert of northwest China that produces heteromorphic fruits and seeds. The primary aims of this study were to characterize the morphology and anatomy of fruits and seeds of this species and compare the role of fruit and seed hetermorphism in dispersal and germination.

Methods

Shape, size, mass and dispersal of siliques and seeds and the thickness of the mucilage layer on seeds were measured, and the anatomy of siliques and seeds, the role of seed mucilage in water absorption/dehydration, germination and adherence of seeds to soil particles, the role of pericarp of lower siliques in seed dormancy and seed after-ripening and germination phenology were studied using standard procedures.

Key Results

Plants produce dehiscent upper siliques with a thin pericarp containing seeds with large wings and a thick mucilage layer and indehiscent lower siliques with a thick pericarp containing nearly wingless seeds with a thin mucilage layer. The dispersal ability of seeds from the upper siliques was much greater than that of intact lower siliques. Mucilage increased the amount of water absorbed by seeds and decreased the rate of dehydration. Seeds with a thick mucilage layer adhered to soil particles much better than those with a thin mucilage layer or those from which mucilage had been removed. Fresh seeds were physiologically dormant and after-ripened during summer. Non-dormant seeds germinated to high percentages in light and in darkness. Germination of seeds from upper siliques is delayed until spring primarily by drought in summer and autumn, whereas the thick, indehiscent pericarp prevents germination for >1 year of seeds retained in lower siliques.

Conclusions

The life cycle of D. strictus is morphologically and physiologically adapted to the cold desert environment in time and space via a combination of characters associated with fruit and seed heteromorphism.     

A new type of specialized morphophysiological dormancy and seed storage behaviour in Hydatellaceae, an early-divergent angiosperm family

Background and Aims

Recent phylogenetic analysis has placed the aquatic family Hydatellaceae as an early-divergent angiosperm. Understanding seed dormancy, germination and desiccation tolerance of Hydatellaceae will facilitate ex situ conservation and advance hypotheses regarding angiosperm evolution.

Methods

Seed germination experiments were completed on three species of south-west Australian Hydatellaceae, Trithuria austinensis, T. bibracteata and T. submersa, to test the effects of temperature, light, germination stimulant and storage. Seeds were sectioned to examine embryo growth during germination in T. austinensis and T. submersa.

Key Results

Some embryo growth and cell division in T. austinensis and T. submersa occurred prior to the emergence of an undifferentiated embryo from the seed coat (‘germination’). Embryo differentiation occurred later, following further growth and a 3- to 4-fold increase in the number of cells. The time taken to achieve 50 % of maximum germination for seeds on water agar was 50, 35 and 37 d for T. austinensis, T bibracteata and T. submersa, respectively.

Conclusions

Seeds of Hydatellaceae have a new kind of specialized morphophysiological dormancy in which neither root nor shoot differentiates until after the embryo emerges from the seed coat. Seed biology is discussed in relation to early angiosperm evolution, together with ex situ conservation of this phylogenetically significant group.     

Axillary bud growth in relation to adventitious root formation in cuttings

Single-node leaf-bud cuttings of Schefflera arboricola Hayata and Stephanotis floribunda Brongn. were set and root formation, onset of axillary bud growth and plant height were measured. An increase in the number of roots in Schefflera, which was achieved with increasing cutting position on the stock plant (measured from top to base) or with increasing stem length below the node, accelerated the onset of axillary bud growth and resulted in an increase in plant height. Increasing the number of roots per cutting in Stephanotis through an increase in basal temperature also accelerated bud and shoot growth. Positional effects on root formation in Stephanotis showed no relationship with axillary bud growth and plant height. A positive relationship between number of roots per cutting and axillary bud growth was found among clones of Stephanotis . In general the results suggest that, with some exceptions, the onset of axillary bud growth is accelerated in cuttings as a result of accelerated root formation and a higher number of roots per cutting.     

Flee or fight uncertainty: plant strategies in relation to anticipated damage

In order to cope with damage, plants have evolved a number of strategies. We incorporate two of those strategies, compensatory regrowth and escaping damage in time, into a mathematical model in an attempt to outline under what circumstances one or the other of these phenotypic traits will evolve. Escaping damage in time is accomplished by flowering and setting seeds at a point of time when the risk of damage is low, whereas a compensatory capacity is made possible by activating a proportion of meristems that are left dormant. Our analysis suggests that damage that is predictable in time will favour phenotypes that flower late in the season and that have a good compensatory capacity. As damage becomes less predictable in time, a strategy that implies flowering as early as possible in the season and with no compensatory capacity at all, becomes advantageous.     

Tuber induction and initiation during production and early field growth of transplants from in vitro-derived potato plants

In transplants from in vitro‐derived plantlets from very early potato (Solanum tuberosum) cultivars, a lower degree of tuber induction at the time of field planting is thought to increase tuber production. Leaf‐bud cuttings were used to assess the progress to tuber induction in in vitro‐derived potato plantlets during the transplant production phase and after subsequent transplanting into the field. Induction and initiation of tubers on the same plants were assessed to study the effects of the duration of transplant production and conditions during transplant production for cv. Gloria (very early) and cv. Bintje (mid‐early). In vitro‐produced plantlets were not induced by the time of planting but rapidly progressed to the induced state thereafter. The progress in induction with time and the change in percentage of plants showing tubers fitted typical sigmoid curves. Plantlets achieved 50% induction ca 15 days after planting into in vivo conditions, and 50% tuber initiation usually occurred 10 days later. Shorter transplant production periods reduced the degree of induction of the transplants at field planting. Transplant production for more than 2 weeks was required to allow conditions during that period to affect induction or initiation. Long‐term non‐inducing conditions delayed the progress to tuber induction in cv. Gloria and delayed tuber initiation in both cultivars. Cv. Gloria showed no faster progress to induction than cv. Bintje but initiated tubers earlier. The results suggest that the relation between progress to induction and tuber initiation is cultivar dependent and that leaf‐bud cuttings can be used successfully in very young in vitro‐derived plants for assessing the progress to tuber induction.