Tetraploid

Genetic improvement  to produce seedless
watermelon offers high quality fruits. This paper describes about
problems related with tetraploid seed germination, various seed
treatment to improve tetraploid seed germination and the
morphological variations observed between the tetraploid and
diploid seeds. Diploid watermelon  seeds of three genetic
backgrounds were treated with colchicine (0.2, 0.3 and  0.4%)
and PEG (0.5%) as an adjuvent. Polyploid watermelon seeds
have poor germination and low seedling vigor mainly due to
thick seed coat and seed coat adherence to emerged cotyledons.
In order to enhance the germination, the tetraploid seeds were
subjected to five different seed treatments i.e; acid scarification,
GA3 treatment, humidification, mechanical scarification and
water soaking for 48hrs. Among the various treatments tested,
maximum germination was recorded in the seeds subjected to
water soaking for 48 hrs in all the three varieties. Tetraploids 
produce less number of seeds per  fruit than those of diploids.
Diploid seeds had complete filled cavity with  embryo whereas
tetraploids developed weak embryo with some empty cavity
hence lower seed germination.

From the first to third growing season in the field test carried out at the Experimental Station of Soybean (Pavlikeni,
Bulgaria) was observed 12 genotypes of red clover, including two Bulgarian diploid varieties Nika 11 (standard) and Sofia
52, four local diploid populations and next six foreign tetraploid varieties, i.e. Kvarta, Astur, Carbo, Elanus, Fregata and
Larus. The goal of study was to determine the effect of ploidity level of the varieties as well as the effect of adaptive
variability of local populations on fresh mass yield, dry mass yields and their persistence in an agro-ecological area with
lower summer moisture assurance for red clover. The highest total dry mass yield was observed for varieties Sofia 52
(2n), Nika 11 (2n), Kvarta (4n) and Astur (4n). The productivity of tetraploids Kvarta and Astur strongly varies depending
on the season and the year, as well as the age of sward. According to the obtained comparative production data for cuts
and years, the tetraploid germplasm has a stronger adaptation to the limiting moisture. In summer drought, typical for the
plains of Northern Bulgaria, tetraploids stop growing and do not compensate for their limited vegetative growth, despite
the excellent moisture guarantee in the late summer, as well as in the spring the next growing season. Local wild-type
germplasm of the species is characterized by a rapid development and lower yield of fresh and dry forage mass compared
to the diploid standard when growing in conditions of optimum moisture but relatively high productivity in the dry
conditions of the summer months. The differences in the genotypic productivity response under dry conditions reported
in this experiment also suggest that the abiotic limit studied can be successfully responded by the genotype factor.

Previous studies have suggested that transgene expression in plants can be affected by ploidy. Here we show that three different transgenes, a reporter transgene, an antisense transgene, and a hairpin RNA (hpRNA) transgene, are all expressed at a lower level in autotetraploid (4n) than in diploid (2n) Arabidopsis. RNA silencing of two endogenous genes was induced by the antisense and hpRNA transgenes and this silencing is significantly less effective in 4n than in 2n Arabidopsis; furthermore, the reduced silencing in 4n Arabidopsis correlated with reduced accumulation of silencing-inducer RNAs. Methylation analysis both of independent 2n and 4n transgenic lines and of 2n and 4n progeny derived from the same 3n transgenic parent, indicated that transgenes are more methylated in 4n than 2n Arabidopsis. These results suggest that transgenes are transcriptionally repressed in the 4n background, resulting in expression levels lower than in the 2n background. Transgenes designed to silence endogenous genes express lower concentrations of silencing-inducer RNAs in 4n Arabidopsis plants, resulting in less effective silencing of target genes than in 2n Arabidopsis plants.