1) Downward growth 
Downward curling of a leaf blade resulting from more rapid cell growth on the upper side of a petiole than on the lower side; often a hyperplastic symptom of plant disease. 
<botany> Asymmetrical growth of a leaf or stem that causes curvature of the structure. ... (18 Nov 1997) ... 
Downward curling of a leaf blade due to cell growth on the upper side of a petiole being more rapid than that on the lower side; often a hyperplastic symptom of plant disease (e.g. the disease caused by potato virus Y in Physalis floridana).Asymmetrical growth of a leaf or stem that causes curvature of the structure.
epinasty, epinastic 1. That phase of vegetable growth in which an organ grows more rapidly on its upper than on its under surface. 2. A downward bending of leaves or other plant parts, resulting from excessive growth of the upper side. In plant physiology, the state in which more vigorous growth occurs in the upper surface of an organ, such as in...
(esp. of leaves) increased growth on the upper surface of an organ or part, causing it to bend downward.