No abstract

A wide range of phenotypic variation was observed among neopolyploids obtained from the diploid pear cultivar 'Fertility' by in vitro colchicine treatment. The variant plantlets had alterations in leaf characteristics. Neopolyploids had significantly different ratios of leaf length to leaf width compared to the diploid control. Shoot regeneration from leaf explants and rooting ability from in vitro shoots of neopolyploids was examined. Regeneration frequencies of shoots from leaf explants of seven of the nine neopolyploids were significantly decreased compared to the diploid control. The organogenic potential of neopolyploids was highly genotypedependent for both shoots and roots. Tetraploid clone 4x -4 failed to regenerate shoots from leaf explants and the pentaploid clone 5x -2 failed to root from in vitro shoots. The results suggest that polyploidization caused the decrease in or loss of in vitro organogenic potential. Regenerated shoots derived from neopolyploids showed different phenotypes, depending on the ploidy of the donor plant.

Pear (Pyrus communis L.) is a nutrient-dense fruit with strong consumer demand and high commercial value. However, most cultivated pear varieties are often susceptible to diseases caused by fungi, bacteria, and viruses. The purpose of the present study was to establish an efficient genetic transformation and regeneration protocol, paving the way for genetic engineering of pear cultivars with enhanced disease resistance. Major factors that influence transformation and regeneration were examined and optimal conditions were established for efficient transformation from leaf explants of 'Old Home', a valuable pear interstem and rootstock. High transformation efficiency was achieved largely due to an improved infection/transformation induction strategy. Co-cultivation of Agrobacterium cells and leaf segments on a liquid induction medium yielded a fivefold increase in transformation frequency. Southern hybridization analysis revealed presence of reporter gene uidA in the genomic DNA samples from independent transgenic plants, confirming the integration of the transgene in recipient pear genomes. The stability of T-DNA integration was evaluated by the consistent presence of the Km selectable marker and the expression pattern of the introduced reporter gene uidA was analyzed by GUS histochemical assay.

Poor adventitious root formation is a major obstacle in micropropagation. In this study, intense efforts have been made for improvement of rooting procedures for triploid, tetraploid and mixploid clones of the pear cultivar 'Fertility' obtained by in vitro colchicine treatment. An efficient rooting procedure has been developed for the pear clones of different ploidy by adding polyvinyl alcohol (PVA) to the rooting medium. PVA significantly improved rooting percentage and root number per plantlet for diploid, triploid and tetraploid clones. However, PVA had little or no effect on rooting capacity of mixploid clones. The efficiency of in vitro rooting in diploid, triploid, tetraploid and mixploid is highly genotype-dependent. In general, diploid was the highest, followed by triploid and tetraploid, mixploid was the lowest.