Twelve genotypes (varieties, hybrids, mutant and hybrid lines) of sorghum (Sorghum bicolor (L.) Moench) were studied. The objective of the study was to determine the popping performance and to establish the relationships with some biochemical parameters (content of crude proteins, starch, moisture) and grain characteristics (pericarp color, grain width, 1000-grain weight). Popping yield of sorghum grain genotypes was in range 32.0% -72.0%. The highest influence on popping yield had 1000-grain weight (r = 0.831), starch content (r = -0.356), followed by moisture content (r = 0.212) and crude proteins (r = 0.282). It was found that the endosperm of the seeds expanded poorly in most genotypes with white coloring of the pericarp (from 33.3 to 90.1%), while for those with a dark-colored seed pericarp, the expansion was from 50.0% to 160.0%. Mutant line M1 (6282) (dark brown color of the pericarp) and hybrid line 1643 (white color of the pericarp) stood out with relatively better popping characteristics and particle size of popped grains. This study demonstrated one of the qualities of sorghum grain-poppability and opportunities for enrichment of the genetic diversity for the breeding program in this culture.

Allelopathic activity of Cuscuta epithymum L. (CVCEY), Cuscuta campestris Yuncker (CVCCA), Phelipanche ramosa (L.) Pomel (ORARA), Phelipanche mutelii (Schultz) Reuter (ORARM) and Phelipanche spp. (PHESS) on germination and initial development of test plats of Lactuca sativa L.cultivar "Great Lakes" was studied under laboratory conditions. It was found that, water exracts of the parasitic weed species in concentrations 0.4, 0.8, 1.6, 3.2, 6.4 and 12.8% w/v have a relatively high inhibitory effect on the seed germination of test plants. The inhibiting rate of parasitic weed species from family Convolvulaceae ranges from 6.24 to 100.0% and for the species of family Orobanchaceae from 42.1 tо 100.0%. Parasitic weed species from family Orobanchaceae (Ph. ramosa, Ph. mutelii and Phelipanche spp.) showed a considerably stronger allelopathic effect (GI average 17.9), as compared with the applied concentrations of water exracts of species from family Convolvulaceae (C. epithymum and C. campestris) (GI average 22.7).

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Changes in some morphological and physiological parameters (leaves/stems ratio, total plastid pigments content, fixed amount nitrogen) of birdsfoot trefoil (Lotus corniculatus L.) (cv. Targovishte 1) and three subterranean clover subspecies, i.e. Trifolium subterraneum ssp. brachycalicinum (cv. Antas), Trifolium subterraneum ssp. yaninicum (cv. Trikkala) and Trifolium subterraneum ssp. subterraneum (cv. Denmark) were studied in a field trial in the Institute of Forage Crops, Pleven, Bulgaria (2012-15). Crops were grown alone (100%) and in mixtures as follows: birdsfoot trefoil + Trifolium subterraneum ssp. brachycalicinum (50:50%); birdsfoot trefoil + Trifolium subterraneum ssp. yaninicum (50:50%); birdsfoot trefoil + Trifolium subterraneum ssp. subterraneum (50:50%). Leaves/stems ratio for alone grown crops was found: birdsfoot trefoil (1.33), Trifolium subterraneum ssp. brachycalicinum (1.02), Trifolium subterraneum ssp. yaninicum (0.93) and Trifolium subterraneum ssp. subterraneum (0.93). Leaves/stems ratio for birdsfoot trefoil in all mixtures was found be higher as compared to alone grown birdsfoot trefoil - by 13.0% for the mixture with Trifolium subterraneum ssp. yaninicum, by 16.3% for that with Trifolium subterraneum ssp. brachycalicinum and by 20.1% for the mixture with Trifolium subterraneum ssp. subterraneum. Total plastid pigments in birdsfoot trefoil increased in all mixtures: with Trifolium subterraneum ssp. brachycalicinum by 7.4%, with Trifolium subterraneum ssp. subterraneum by 8.1% and with Trifolium subterraneum ssp. yaninicum by 15.6%. From mixtures of birdsfoot trefoil were obtained more fixed amount of nitrogen - from 1.71 kg N/da (with Trifolium subterraneum ssp. subterraneum) to 4.84 kg N/da (with Trifolium subterraneum ssp. brachycalicinum) as compared to alone grown birdsfoot trefoil. Birdsfoot trefoil and subterranean clover in mixtures showed good tolerance, morphological and physiological status.