ABSTRACT/The purpose of our research was to identify shrub species growing in southern Quebec that inhibit ecological succession in power-line corridors. Results are presented in three parts. First, clonal characteristics that allowed the establishment of stable communities were identified. Second, successional vector analysis identified those species that have the potential to inhibit succession.In poorly drained sites those species were Comus stolonifera, C. obliqua, Salix petiolaris, and Spiraea alba. In well-drained sites, those species were Zanthoxylum americanum, Rubus idaeus, Spiraea alba, Rhus typhina, and Thuja occidentalis. Third, analysis of variance showed that there is a significantly larger number of tree seedlings found in adjacent herbaceous communities than found under the dense cover of Comus stolonifera, C. obfiqua, Salix petiolaris, Spiraea alba, Rhus typhina, Rubus idaeus, Thuya occidentafis, and Zanthoxylum americanum. These results indicate that the planting of selected shrub species could, through biological control, delay reforestation.

/ The use of relatively stable shrub communities to control invasionby trees could be an efficient way of reducing herbicide applications, andthus represents an environmental gain, in areas such as rights-of-way. Thequestion is how to favor the expansion of these relatively stable shrubcommunities using different propagation techniques. Three experimentaltreatments, cutting back, layering, and cutting back-layering were performedon Cornus stolonifera, Salix petiolaris, and Spiraea albaclones already located within the corridor of an electrical power line. Toestablish the efficiency of treatments, we examined the statisticaldifferences of growth traits between species and treatments.An analysis of the effects of layering shows, after the first growth season,differences for all growth traits in only one species, Spiraea alba.After the second growth season, we observed the development of new aerialstems. Layering favors horizontal expansion of shrubs over heightdevelopment. The third year after treatment, the effect of layering isreduced except for Cornus stolonifera, which continuously increases,as shown by the significant progression of the clone issued from the layereven five years after treatments. With the cutting back technique, weexpected a distinct vertical growth of the shrubs at the expense ofincreasing the crown diameter. This technique would be best associated withthe rejuvenation of clones, followed by a layering of new shoots to allow ahorizontal expansion of the shrubs. Therefore, the formation of a dense shrubcommunity by layering should be considered a valuable approach for thebiological control of undesirable trees in powerline rights-of-way.KEY WORDS: Layering; Cutting back; Right-of-way; Cornus stolonifera;Salix petiolaris; Spiraea alba; Quebec

Two diploid clones of self-incompatible Solanum chacoense Bitt. with androgenetic ability were tested for anther and leaf disc culture response together with eight of their reciprocal F1 hybrids. Large differences were found among genotypes in frequency of anther induction as well as in the phase of plant regeneration. Anthers harvested in June showed a significantly higher percentage of response (17.5%) at the induction phase than those collected in July (13.8%) or August (12.7%). The lowest induction frequency was observed in May (7.3%). By contrast, plant regeneration from induced anthers did not vary during this time. Genotypic differences were also observed in leaf disc response. The two parental clones and two of their hybrids failed to produce any shoots. Among the remaining genotypes, two had only sporadic occurrence of shoot formation, two gave an intermediate response (15% and 24% of their discs carried shoots), whereas the discs of the two remaining genotypes responded well to culture (68% and 77%). The genetic analysis performed on the reciprocal hybrids revealed that a positive significant correlation existed between anther induction and leaf disc response (Spearman's r = 0.82; p = 0.01). This suggests that, under our conditions, these two aspects of tissue culture might share a common system of genetic control. Estimates of broad sense heritabilities, for leaf disc culture, 83% were obtained and the number of effective factors involved in the control of tissue culture response, indicated a relatively simple genetic control. Finally, considering the potentialities opened by the use of RFLP analysis, it might be possible to find probes that are linked with genes involved in tissue culture competence.

No abstract