2019 ASHS Annual Conference

Irradiation generates random variation, resulting in mutant plants with new morphological traits. Preliminary research in our lab on Pavonia hastata showed a curvilinear response of seed germination to radiation dosages between 0 to 800 Gy. Since P. hastata can tolerant high rates of irradiation, a study was initiated with three species of Pavonia (P. hastata, P. lasiopetala, and P. missionum) treated at Cobalt-60 irradiation at rates of 0 Gy, 200 Gy, 400 Gy, 600 Gy, 800 Gy, and 1,000 Gy. Four replicates for each treatment and 50 seeds for each replicate were planted. Similar to many genera in the Malvaceae, the genus Pavonia has impervious mericarps which inhibit the uptake of water. Scarification with concentrated sulfuric acid was applied for 10 min on seed of all three species to break the physical dormancy caused by the mericarp. The effect of scarification was observed using Scanning Electron Microscopy (SEM). A preliminary study in 2018 indicated that seed germination of P. hastata showed responded linearly to radiation dosages from 0 to 1,000 Gy. The control (0 Gy) had highest germination percentage (58%) after 31 days whereas germination at 1,000 Gy was 34%. Germination percentages were randomly distributed for P. lasiopetala with the highest germination percentage (85%) occurring at the 800 Gy treatment. P. missionum was the most vigorous among the three species with over 90% germination for four irradiation levels (0 Gy, 200 Gy, 400 Gy, and 800 Gy) and over 60 % germination for two irradiation levels (600 Gy and 1,000 Gy). Interestingly, 64% germination was observed for P. missionum at the 1,000 Gy treatment, but the seedlings remained at the cotyledon stage until the end of the study. Only three seedlings at 1,000 Gy survived after three months. Irradiated plants were transplanted to 2.8 l pots and grown for further evaluation. Seed from the irradiated plants (M1 – first mutant generation) were collected and will be grown in 2019 since mutations are usually seen in M2 generation. The seed germination study will be repeated in 2019.