コウサクチ ニ オケル オオバコ PLANTAGO ASIATICA L. ノ テイチャク ニ オヨボス ヒキヌキ フクド ノ エイキョウ

Abstract

オオバコは畦畔および農道では旺盛に繁殖するが,耕起地では繁茂しないことが知られている。その要因を解明するため,オオバコおよび比較植物としてメヒシバ,オヒシバおよびスベリヒユを用いて,耕耘を想定した引抜き,埋没処理に対する再生反応,および耕耘後の種子再生産能力推定のための播種期別生殖成長到達日数について検討した。実験1として,3および5葉期の個体を引抜き後,あるいは引抜かずに,それらの個体を深さ2および6cmに土壌で埋没した。対照区には,引抜きおよび埋没をしない区を当てた。その結果,6cmの埋没区においては,引抜きの有無,処理の時期にかかわらず4種とも全く再生しなかったが,2cmの埋没区では,再生程度に著しい種間差があった。オオバコでは無引抜き区において,対照区の3%(3葉期処理)∼17%(5葉期処理),スベリヒユでは引抜き区で3%(3葉期処理)∼27%(5葉期処理),無引抜き区で13%(3葉期処理)∼27%(5葉期処理),メヒシバでは引抜き区および無引抜き区それぞれ3%(3葉期処理)∼7%および20%(5葉期処理),オヒシバでは5葉期の引抜き区のみ3%が再生した。再生個体の草丈は,オオバコにおいて劣った。実験2として,5∼7月に播種したところ,7月播種のオオバコのみ当年内には生殖成長に至らなかった。以上のように,オオバコ個体は耕耘時に土壌から引抜かれ,土壌中に埋没されると全く再生できず,引抜かれなくても土壌埋没によって再生が劣り,草丈も低く,さらに,季節的に遅く出芽した個体では種子生産が当年内に行われず,耕地において生活環の完結が困難になるものと推察された。Asiatic plantain (Plantago asiatica L.) grows thickly and rapidly in levees and farm roads, but not in cultivated fields. We clarified the non-adaptability of Asiatic plantain to fields that had been plowed for management.Generally, plowing pulls up, cuts, and buries plants under the soil. The experiment described herein investigates regrowth responses against artificially simulated “pulling-up” and “soil covering” caused by plowing. Assuming that germination from buried seeds occurs after plowing, florescence occurring within a year from seed sowing was examined. Asiatic plantain was examined along with upland weeds : hairy crabgrass (Digitaria adscendens (H.B.K.) Henr.), goosegrass (Eleusine indica (L.) Gaertn.), and common purslane (Portulaca oleracea L.).Plants in three-leaf and five-leaf stages were pulled up and covered with 2cm or 6cm deep soil. For comparison, plants that had not been pulled up were treated without soil covering (established plants hereinafter).Results show that none of the four plants with soil covering thickness of 6cm regrew. However, with 2-cm-thick coverage, considerable differences were apparent among species. Regarding Asiatic plantain, only 3% (three-leaf stage treatment)-17% (five-leaf stage treatment) of established plants regrew. Regarding common purslane, 3% (three-leaf stage treatment)-27% (five-leaf stage treatment) of the plants regrew when pulled up ; 13% (three-leaf stage treatment)-27% (five-leaf stage treatment) of plants regrew with no pulling-up treatment. For hairy crabgrass, 3% (three-leaf stage treatment)-7% (five-leaf stage treatment) of plants regrew with pulling-up treatment ; 20% of plants regrew in the five-leaf stage with none in the pulling-up treatment. Furthermore, only 3% of the goosegrass pulled up at the five-leaf stage regrew. The regrown Asiatic plantain plant length was considerably less. Of the four species sown in May, June, and July, only the Asiatic plantain did not flower within the year sown in July.As described above, Asiatic plantain, once pulled up from the soil, is unable to regrow. Plants that are covered with soil, even if established, are very small. Seedlings that germinate in the late season (summer) have insufficient time to produce seed. These results underscore that Asiatic plantain cannot complete its life cycle in a frequently plowed field