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In the oasis of Tozeur (Tunisia) a peculiar date palm ploidy chimera was discovered, showing a diploid (2n = 2x) and a tetraploid (2n =4x) sector and a uniform tetraploid offshoot. This chimera allowed to describe the effects of chromosome doubling on some selected features. Because both ploidies occur within one plant, there was no environmental bias. Tetraploid leaves are longer, bear larger leaflets and spines and have a thicker rachis than normal diploid leaves. During three seasons, tetraploid inflorescences appeared ten days later than their diploid counterparts. The tetraploid sector formed bunches with stalks bearing larger fruits, with a higher percentage of inedible parthenocarpic fruits, than bunches that arose from the diploid sector. Tetraploid fruits are significantly longer, wider and heavier than diploid fruits, with a larger pulp diameter, irrespective of whether they are seeded or parthenocarpic. Diploid parthenocarpic fruits are longer than seeded fruits, while tetraploid parthenocarpic and seeded fruits both show the same size. The occurrence of tetraploidy opens new perspectives in date palm breeding. Pollination of tetraploid pistils with pollen from diploid males gave rise to a relatively low number of triploid plantlets, suggesting a triploid block.

Monospore cultures of rose powdery mildew (Sphaerotheca pannosa var. rosae) were established from isolates collected on outdoor grown roses at different locations in Belgium. These monospore cultures were tested on rose cultivars and species with different levels of natural resistance to examine the possible existence of different pathotypes. Therefore a screening protocol including scoring after artificial infection was developed on in vitro plantlets. The calculated disease indexes of the collected monospore cultures on different rose cultivars and species showed that up to now in the collected isolates no evidence of distinct pathotypes could be found. The reaction of plants towards the disease differed greatly between the examined cultivars and species. The test was validated for in vivo circumstances indicating that in vitro rose plants can be used for pathotype and resistance screening.