筆者らが最近開発したウンシュウミカンの周年マルチ点滴灌水同時施肥法 (マルドリ法と略称) では, 根域は年間を通して透湿性マルチ下に置かれ, 点滴チューブを用いて灌水施肥管理が行われる. 本試験においては, このようなウンシュウミカンの慣行栽培とは大きく異なる地下部環境が細根に与える影響について, いくつかの知見を得た. マルドリ法で3年間栽培されたウンシュウミカンにおける点滴孔直下では白い細根が密生しており, それらの細根径は慣行栽培樹ならびにマルドリ栽培樹の点滴孔から離れた位置における細根径よりも細いものであった. また, 点滴孔直下の細根の呼吸活性は慣行栽培樹の細根よりも高いことが明らかとなるとともに, マルドリ栽培樹の点滴孔から離れた位置の細根の呼吸活性も慣行栽培樹の根と比較して有意に高いものであった. これらの結果から, マルドリ栽培3年目のウンシュウミカンの細根は慣行栽培以上に健全であり, 呼吸活性の高い細い細根が増えることからマルドリ法が樹勢の維持に寄与するものと考えられる.

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The cortex is the basic part of the primary root body and represents an important constituent of the root, both structurally and functionally. In monocotyledons, it might persist during the entire life of the root. In dicotyledons, with limited secondary thickening it might persist for a long time and be subject to dilatation growth. In intensively secondary-thickening roots, the cortex gradually deteriorates and is replaced by secondary tissues-the periderm. The functions of cortical tissues are diverse. The endodermis, and to some extent the exodermis, represent apoplastic barriers that control the uptake and radial transport of water and solutes by the root. However, these layers have several additional functions such as mechanically protecting the stele and protection against pathogens and parasites. Although the mid-cortex (or mesodermis) is primarily the site for reserve material deposition, it can also have several different functions that depend on the species and growth conditions. These include aeration in hypoxia (aerenchyma formation), and the location for symbiosis and even photosynthesis. The cortex varies widely amongst species and even in various root types of the same species. It might be designated as a root buffer zone, especially under stress conditions. Some aspects of the development, structure and function of cortical tissues are discussed in this report.

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