Yasuhiro Kono

Effects of soil compaction on the development of rice and maize root systems

Abstract The aim of this study was to determine the effects of soil compaction on the development of root system components of rice ( Oryza sativa L.) and maize ( Zea mays L.). Plants were grown for 4 weeks in root ☐es (24 cm long × 2 cm wide × 40 cm deep) with soil bulk densities of 1.33 g/cm 3 (control) and 1.50 g/cm 3 (compact). In the compact treatment the main root axes of rice never penetrated beyond the 10–15 cm soil layer even by the fourth week, while seminal and seminal adventitious roots of maize had penetrated 30–35 cm deep by the third week. Generally, growth of higher order (second and third) lateral roots compensated for the restricted growth of the main root axes in both species. The ratio of first order L-type laterals producing higher order laterals on their axes was greater in the compact treatment for rice, while that of maize was not significantly increased. The root growth responses of rice and maize to soil compaction were different in the downward penetration of the main axis and the growth of the higher order laterals.

Response of the different root system components of sorghum to incidence of waterlogging

Crop plants are often exposed to excessive soil moisture conditions during growth. Sorghum plants (Sorghum bicolor Moench) were grown in pots and subsequently subjected to continuous waterlogging during their vegetative stage to determine the growth and development of the different root system components. Plants grown in well-drained pots served as controls. Other plants were subjected to different timings of waterlogging, i.e. early (waterlogged during the early part of their vegetative growth) and late (waterlogged during the late part of their vegetative stage). All plants were kept under glasshouse conditions. Root and shoot development was measured by destructive sampling. Continuous waterlogging caused an immediate increase in the number of nodal root (NR) axes but not their total length. All other root system components such as NR laterals and the seminal root (SR) and its laterals had their number and length markedly restricted by waterlogging. NR production appeared to be an adaptive response of sorghum to waterlogging. In the event that NRs in the lower nodal position of the plants stem died due to waterlogging injury, new NRs appeared in the next higher nodal position, suggesting a relationship between the death of older NRs and the production of new ones. The trends of NR lateral production followed that of the NR axes. Waterlogged plants generally showed a small root system and limited shoot growth. In early-waterlogged plants the NR and their laterals regrew actively after they were removed from waterlogged conditions and allowed to grow under drained conditions for 9 days. In the late-waterlogged plants NRs continued to increase in number and length while other components were inhibited. The SR and its laterals did not show any evidence of active regrowth in the early or late waterlogging treatments. Plant recovery from waterlogging was brought about mainly by the resumption of growth of the NRs, i.e. elongation of existing functional axes and initiation of new laterals.

Epidermal cell elongation in sorghum seminal roots exposed to high root-zone temperature

Abstract The nature of inhibition of seminal root elongation in sorghum ( Sorghum bicolor Moench) plants grown under different periods of high root-zone temperature (RZT) of 40°C was analyzed by measuring the epidermal cell lengths at fixed points along the growth zone. Cell lengths of roots exposed to high RZT were significantly shorter than those grown at 25°C. Growth in cell lengths became more inhibited as the period of exposure to high temperature was increased. Cell elongation peaked closer to the apex as the period of exposure to high RZT increased. Reduction of the elongation region was 10–16% for every 2 days of growth under high RZT. The total number of epidermal cells added to a cell fine per hour (cell flux), estimated from epidermal cell lengths and root elongation rates, was reduced by 26% for every 2 days of exposure to the high RZT.

Specific colonization of the hypodermis of sorghum roots by an endophyte, Polymyxa sp.

Abstract A number of clusters of resting spores of an endophyte were found to have colonized the nodal root axes and first order lateral roots of sorghum at the heading stage. The clusters with a diameter ranging 15 to 20 μm consisted of a number of spores with a diameter in the range of 2 to 5 μm. Based on the morphological characteristics, the endophyte was tentatively assigned to Polymyxa sp. The clusters were distributed in the epidermis and the hypodermis, but mostly in the latter. The clusters were absent in the tissues internal to the hypodermis. The number of cells colonized by the clusters in the hypodermis, the hypodermal cell lignification identified by the phloroglucinol-HCl test, and the cortical sclerenchyma development were examined acropetally in three nodal roots which emerged from the third node. The colonized cells accounted for less than about 10% of the total number of the hypodermal cells in the first 8 cm portion, but beyond this part, their number increased and they accounted for 1...