Shoot and root interference of morning glory on the initial growth of sugarcane

ABSTRACT Among weeds, morning glories comprise a very important group of climbing plants that infest sugarcane crops. The objective of this study was to evaluate the shoot and root interference of Merremia cissoides on the initial growth of sugarcane cultivar RB 966928. The experiment consisted of five treatment groups: (i) sugarcane monocropping, (ii) morning glory monocropping, (iii) sugarcane intertwined with morning glory but inseparate boxes, (iv) sugarcane intertwined with morning glory in attached boxes and (v) sugarcane with morning glory in attached boxes with morning glory prevented from intertwining with the sugarcane. The experimental design consisted of randomized blocks with four replicates. Merremia cissoides adversely affected the initial growth of the RB 966928 sugarcane starting at 90 days after transplanting (DAT). This effect increased with the time of intercropping, reaching at 180 DAT with a reduction of 57.3% in height,15.5% in stalk diameter, 90.4% in leaf areas, 86.6 and 75.2% in stalk and leaf dry mass, respectively. These reductions primarily due to the weed intertwining with the sugarcane plants because the weed had a physical choking and shading effect. This negative effect of morning glory on the sugarcane plants increased when they shared the substrate (i.e., when they competed for space and water), which also adversely affected weed growth, reducing 50.2% leaf areas and 42.1% shoot dry mass. The leaf area and the stalk and leaf dry mass of sugarcane are the characteristics more sensitive to the weed interference. Thus, both the shoot and root of M. cissoides interferes negatively in the growth of sugarcane, with the effect proportional to the period of coexistence, highlighting the detrimental effect on the stem (greater economic interest), and may also compromise the mechanical harvesting of the crop.摘要 在杂草类群中，牵牛花（morning glory）是一类为害甘蔗作物的重要攀援杂草。本研究旨在评估盒果藤（Merremia cissoides）的地上部与地下部对甘蔗品种RB 966928初始生长的干扰效应。试验共设置5个处理组：(i) 甘蔗单作；(ii) 牵牛花单作；(iii) 甘蔗与牵牛花缠结但分箱种植；(iv) 甘蔗与牵牛花缠结且共箱种植；(v) 甘蔗与牵牛花共箱但牵牛花被阻隔无法缠结甘蔗。试验采用随机区组设计，设置4次重复。 盒果藤在移栽后90天（days after transplanting, DAT）起即对RB 966928甘蔗的初始生长产生不利影响，且该抑制作用随间作时长增加而增强：至移栽后180天时，甘蔗株高降低57.3%、茎径降低15.5%、叶面积降低90.4%、茎干重与叶干重分别降低86.6%和75.2%。此类抑制作用主要源于杂草缠结甘蔗植株所产生的物理挤压与遮阴效应。当二者共享栽培基质（即竞争空间与水分）时，牵牛花对甘蔗的负面效应进一步增强，同时也会抑制自身生长，使其叶面积降低50.2%、地上部干重降低42.1%。甘蔗的叶面积、茎干重与叶干重是对杂草干扰最为敏感的性状。 综上，盒果藤的地上部与地下部均会对甘蔗生长产生负面影响，且效应强度与二者共存时长呈正相关；其对甘蔗茎秆（经济价值核心部位）的不利影响尤为突出，同时还可能对作物的机械采收造成不利影响。