Effects of Pre-Planting Soaking on Growth and Survival of Black Willow Cuttings

Black willow (Salix nigra) uses periodic flood events for dispersal of vegetative propagules, subjecting them to periods of soaking before their deposition along the streambank. It was hypothesized that this life history trait results in optimal conditions for willow growth and survival. To test this hypothesis, a greenhouse experiment was conducted using 1.2‐m‐long black willow cuttings (posts) with a basal diameter of 5 cm. Cuttings were subjected to three soaking treatments (0, 3, and 10 days) and then grown under four soil moisture regimes (control, drought, permanently flooded, and intermittently flooded). Growth, biomass, and survival were recorded. Results showed that soaking posts for 10 days was most beneficial in the control soil moisture regime, enhancing root, shoot, leaf, and total biomass production. Shoot abundance and growth were also enhanced by 10 days of soaking in the control and permanently flooded moisture regimes. Finally, survival increased significantly in control and drought moisture regimes in response to the 10‐day soaking treatment. Results clearly demonstrated that soaking had significant effects on willow post success when evaluated across all soil moisture regimes. Posts subjected to the 10‐day soaking treatment consistently had greatest growth and biomass and displayed a doubling of the survival rate. Therefore, soaking willow cuttings before planting is a simple, inexpensive technique that may be used to bolster streambank restoration success.     

Seasonal pattern of accumulation and effects of low temperatures on storage compounds in Trifolium repens

The seasonal pattern of concentrations of nitrogen, starch and vegetative storage protein (VSP) in stolons of Trifolium repens L. grown in the field were studied. Two different genotypes, cv. Aran and cv. Rivendel, differing in their morphology (stolon thickness and branching rate) but with similar growth rates, were used. Maximum concentrations of starch were found in summer whereas hydrolysis of starch took place throughout winter, suggesting that C storage is more important for winter survival than for promotion of early spring growth. On the other hand, VSP and nitrogen accumulated in autumn and early winter and then decreased when growth was resumed during early spring. For both cultivars, an inverse relationship was found between VSP concentration in stolons and mean air temperature, suggesting that VSP accumulation may be triggered by low temperature. Further experiments with plants grown under different regimes of temperature and daylength, suggested that VSP synthesis is stimulated by low root temperatures, with a slight synergistic effect of short daylength.
The effects of root temperature on growth, N₂ fixation, NH₄⁺ uptake and N allocation within Trifolium repens L., were studied under controlled conditions. The shoot growth rate was greatly reduced when root temperatures were lowered from 12 to 6°C, while the rate of stolon growth was less affected. Low root temperatures inhibited N2 fixation more than it did NH₄⁺ uptake, but the relative allocation of N to stolons was increased. Lowering root temperature also increased the accumulation of VSP in stolons. These results are discussed in terms of the mechanism associated with low temperature stimulation of VSP accumulation and its coupling with changes in the source/sink relations for allocation of N, between growth and storage.     

Lack of effect of photoperiod on metabolism of exogenous GA19 and GA1 in Salix pentandra seedlings

The effect of photoperiod on metabolism of 16,17-[³H₂]GA₁₉, and 1.2-[³H₂]GA₁ applied to intact seedlings of Salix pentandra, was investigated. No difference was found in conversion of 16,17-[³H₂]GA₁₉ to 16,17-[³H₂]GA₂₀, and 16,17-[³H₂]GA₁, or in metabolism of 1,2-[³H₂]GA₁ to [³H]GA₈ between plants grown in continuous light and plants exposed for 14 days to a 12-h photoperiod. Also, leaf discs from plants grown in long or short days, converted 16,17-[³H₂]GA₁₉ both in light and darkness. These data on metabolism of 16,17-[³H₂]GA₁₉, contrast with previous results, which have indicated a photoperiodic control of the metabolism of GA₁₉ to GA₂₀ in S. pentandra. Presence of these applied labelled GAs and their metabolites in different parts of seedlings was recorded, after application to intact seedlings as well as to isolated plant parts. When 16,17-[³H₂]GA₁₉ was applied through the roots of intact plants, the relative amounts of 16,17-[³H₂]GA₁ present in leaves and shoot apices were higher than in roots and stems. In corresponding experiments with 1,2-[³H₂]GA₁, relatively higher amounts of [³H₂]GA₈ were found in roots and stems than in leaves and shoot apices. Twenty-four hours after application of 16,17-[³H₂]GA₁₉ to isolated plant parts, 16,17-[³H₂]GA₂₀ and 16,17-[³H₂]GA₁ were found in leaves and roots, but not in internodes. Incubation of isolated plant parts with 1,2-[³H₂]GA₁ for 24 h resulted in presence of [³H]GA₈ in all parts. The results mentioned above were obtained by monitoring metabolites by HPLC with on-line radio counting. The conversions of 17-[²H₂]GA₁₉ to 17-[²H₂]GA₂₀ and 17-[²H₂]GA₁ in shoot apices and whole seedlings, and of 17-[²H₂]GA₈ in whole seedlings, were confirmed by GC-MS.     

Development of a fertile genetic bridge between Trifolium ambiguum M. Bieb. and T. repens L.

  Trifolium ambiguum M. Bieb and T. repens L. are taxonomically related but very difficult to cross. The rare hybrids so far reported between these two species were obtained only by embryo culture. This difficulty has been overcome in the present research by the creation of a “fertile bridge” between T. ambiguum and T. repens. Characters of interest can now be transferred from T. ambiguum to T. repens by using this “fertile bridge” without the use of sophisticated techniques. An array of backcross progenies was generated from crosses between a T. ambiguum×T. repens F₁ hybrid (8x H-435) and its parental species. The 8x hybrid was cross-fertile only with T. repens and resulted in 145 seeds from 1578 reciprocal crosses. Eleven of nineteen initially grown BC₁F₁ plants were all hexaploid with an average pollen stainability of 41.6%. A high frequency of multivalents at metaphase-I indicated that both autosyndetic and allosyndetic pairing occurred. Backcrosses of 6x BC₁F₁ plants to T. repens resulted in 5x BC₂F₁ plants with an average pollen stainability of 59.3%. On the other hand, 6x BC₁F₁×6x T. ambiguum crosses did not produce any seed and only two pentaploid plants were obtained from 6x BC₁F₁×4x T. ambiguum crosses. The difficulty encountered in generating 6x backcross progeny with 6x T. ambiguum was overcome by intercrossing the 6x BC₁F₁ plants and producing 6x BC₁F₂ plants with an average pollen stainability of 65.8%. One of these 6x BC₁F₂ plants was cross-compatible as a female with 6x T. ambiguum and resulted in CBC₂ plants that were all cross-compatible with 6x T. ambiguum. The 6x BC₁F₂ plants are likely to be superior to 6x BC₁F₁ progeny, as they have exhibited better expression of the combined rhizomatous and stoloniferous growth habit, improved fertility, more frequent nodal rooting and heavier nodulation. Consequently, the 6x BC₁F₂ plants can either be used directly in the selection programme or as a “fertile bridge” between the two parental species. The present work has resulted in the development of a series of fertile hybrids by the manipulation of chromosome numbers, combining the agronomic characteristics of the parent species in varying genome balances and at a range of ploidy levels. It is concluded that the initial sterility of the primary interspecific hybrids need not be a barrier to successful inter-breeding. Received: 2 August 1996 / Accepted: 4 April 1997     

Resurrection of Rabdophaga salicivora Shinji (Diptera: Cecidomyiidae), a Japanese gall midge formerly misidentified as a North American species, Rabdophaga rigidae (Osten Sacken), with observations on the phylogenetic relationships of its populations in Japan and the Russian Far East

Intercontinental biotic connections between Eurasia and North America are common in many gall midge genera (Diptera: Cecidomyiidae), but only a few species have been recorded from both continents. In Japan, four gall midge species had been previously considered to be identical to North American species, but three of these cases have already been disproved. We examined the remaining species, Rabdophaga rigidae, which had been originally described from Japan as Rabdophaga salicivora in 1938, later recorded from the Russian Far East in 1967, and synonymized with a North American species, R. rigidae, in 1982. Morphological features and partial sequence data of the mtDNA cytochrome oxidase subunit I (COI) region suggested that the Japanese species is a distinct species and is identical to the species recorded from the Russian Far East. We therefore apply the original name, R. salicivora, to the Japanese and the Russian species. In addition, on the basis of a molecular phylogenetic analysis, we conclude that R. salicivora possibly came to the Japanese Archipelago through the Korean Peninsula and established itself first in the southern parts of Japan. Then, it expanded its distribution range to northern parts of Honshu, but could not reach Hokkaido, probably because of the Tsugaru Strait between Honshu and Hokkaido.     

Nitrogen homeostasis in a willow leaf beetle, Plagiodera versicolora, is independent of host plant quality

While foliar nitrogen (N) content of host plants depends on environmental conditions, N content of herbivorous insects may remain relatively constant due to homeostasis. However, it is unknown to what extent insects can maintain their body elemental composition against natural variation in host plant quality. The present study examined the performance and N content of a willow leaf beetle, Plagiodera versicolora Laicharting (Coleoptera: Chrysomelidae), when fed leaves of host willow, Salix eriocarpa Franchet et Savatier (Salicaceae), with varying nutritional status. Water content, toughness, and N content of willow leaves varied seasonally, and they affected performance of the leaf beetle. The leaf beetle achieved high performance when fed young leaves. On the other hand, the N content of the leaf beetle changed little, and it was independent of that of willow leaves, indicating strong N homeostasis of the leaf beetle. We discussed the function of N homeostasis in herbivorous insects in tritrophic level interactions.     

甘肃柳属一新种

灌木,高约1.5m;当年生小枝被淡黄灰色丝状长柔毛,去年生枝多少被毛;芽光滑无毛。叶圆形、宽椭圆形或倒卵圆形,长1.5-2.5(-3) cm,宽1.2-2cm,先端圆形,基部圆形或近圆形,全缘,腹面暗绿色,无毛,背面淡绿色,密被丝状长柔毛,侧脉5-7对,网脉在背面明显;叶柄长0.2-0.4cm,被丝状长柔毛。花枝长1-1.2cm,被丝状长柔毛,具2-3枚正常叶