Kang-Bo Shim

Yield of maize ( Zea mays L.) logistically declined with increasing length of the consecutive visible wilting days during flowering

Under future climate conditions, the frequency and severity of drought are expected to increase. Maize (Zea mays L.) is susceptible to drought, especially at flowering. The objective of this study was to investigate the effect of consecutive days of visible wilting (DAW) during tassel emergence using two types of Korean maize hybrids, Gwangpyeongok (Gwp; normal) and Ilmichal (Ilmi; waxy). Traits related to plant growth and yield were measured at harvest. Drought stress during tassel emergence significantly reduced the number of green leaves per plant. Silking was delayed due to drought stress during the stage of tassel emergence, although anthesis was only slightly affected, which resulted in an increase in the anthesis-silking interval (ASI). For each DAW, ASI increased by 1.6 days and 0.8 days for Gwp and Ilmi, respectively. The number of green leaves and ASI showed strong correlation with DAW length and grain yield, which suggested that those factors may be selective traits for drought tolerance at flowering. The filled grain number per plant declined logistically with increasing DAW due to reductions in kernels per row and percentage of filled grains. The filled grain number per plant significantly declined starting at 5 and 10 DAW in Gwp and Ilmi, respectively, which indicated that drought stress effects are dependent on drought severity and the genetic characteristics of specific hybrids. Probit analysis revealed that DAW causing 50% reduction in maize grain yield was about 4.7 and 6.3 days in Gwp and Ilmi, respectively, which resulted in about 13.6% and 9.2% reduction in grain yield per day of DAW, respectively. These results indicate that Gwangpyeongok is more sensitive to drought stress during flowering than Ilmichal.

Changes in cuticular waxes of developing leaves in sesame (Sesamum indicum L.).

Sesame (Sesamum indicum L.) is one of the most important oil seed crops, which has been used as a traditional health food. The objective of this study was to investigate the changes of leaf cuticular waxes during plant growth from 5 to 75 days after seedling emergence, and the variation of leaf waxes with different leaf position; top, middle, and lower positions, using four Korean sesame cultivars, Ahnsan, Danbaeck, Hanseom, and Kyeongheuk. Alkanes in lower leaves and aldehydes in top leaves among leaf positions were the most abundant, with alkanes being with major portion in all leaf position of four sesame cultivars. Total leaf wax load decreased around three-fold between 5 and 30 days, and then remained constant up to day 75. The percentages of alkanes and aldehydes increased between 5 and 15 days and then changed little or increasingly, showing minor variation depending on sesame cultivars. The rate of increase of alkanes was slightly higher than that of aldehydes. Chain length of alkanes and aldehydes became longer from 5 to 30 days, and then remained almost constant till day 75. The major homologue in alkanes was the C29 at day 5 and the C33 constituent after day 30, while the major homologue in aldehydes was the C32 constituent continuously during leaf development. The results demonstrated that the chain length for alkane and aldehyde constituents changed increasingly by chain elongation and wax biosynthesis during leaf development of sesame.

Impact of the consecutive days of visible wilting on growth and yield during tassel initiation in maize ( Zea Mays L.)

Maize (Zea mays L.) is a major crop with different uses but shows significant susceptibility to drought stress. Recent climate change has caused prolonged drought stress, but in most countries maize production relies on rain-fed cultivation. This study was to investigate the impact of the consecutive days of visible wilting (DAW) during tassel initiation (V6) using two types of Korean maize hybrids, Gwangpyeongok (GWP) and Ilmichal (Ilmi). The traits related to plant growth and yield were measured at harvest. Drought stress during tassel initiation linearly reduced plant elongation and dry matter accumulation with the length of DAW increasing but did not affect the leaf number per plant. Our results from the simple linear regression analysis indicated that silking of GWP and Ilmi would be delayed by 0.78 and 0.61 days per DAW, respectively, which was similar to anthesis. Still, little change was observed for interval between anthesis and silking under the same condition. The kernels per row were very dependent on the length of DAW but the rows per ear were not. The percentage of filled grains and the 100- grain weight were significantly reduced only at 15- or 20-DAW and more markedly so in Gwangpyeongok at 20-DAW. The filled grain number per plant showed a gradual logistical decline mainly due to decreases in the kernels per row. All these reductions may be because initiation and growth of tassel, ear, and kernels and internode elongation beginning around V6 are sensitive to water deficits. Probit analysis revealed that the DAW to cause 50% reduction in plant grain yield was about 12 and 20 days in GWP and Ilmi, resulting in about 4.5 and 2.7% reduction a day of DAW, respectively. These results indicate that Gwangpyeongok may be more sensitive to drought stress during tassel initiation than Ilmichal.

Evaluation of waterlogging tolerance with the degree of foliar senescence at early vegetative stage of maize ( Zea mays L.)

Maize is highly susceptible to waterlogging, which is becoming one of worldwide abiotic threats in many agricultural areas. This study was evaluated to establish the screening method and to find tolerant maize genotypes. Six Korean maize inbred lines were subjected to waterlogging at V3 for 15 days using a big size pot with single maize plant (big pot method) and a box containing 31 maize plants at a time (box method). The degree of foliar senescence and the number of senescent leaves were better indicators for selecting waterlogging tolerant maize genotypes than SPAD value and plant height. The degree of foliar senescence revealed that KS124, KS140, and KS141 are tolerant, and KS85 is susceptible to waterlogging at the early growth stage. These responses of foliar senescence were in clear accordance with those of plant grain yield, which was supported by stress tolerance index for grain yield. The box method also showed the similar response of foliar senescence to the big pot method. Therefore, this box method based on foliar senescence may be simple and efficient for large-scale screening of maize germplasm against waterlogging stress. It was concluded that foliar senescence can be a good indicator for selecting tolerant maize genotypes against waterlogging at the early growth stage.