AOBPreview originally published online on May 21, 2004
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Annals of Botany 94: 179-186, 2004
© 2004 Annals of Botany Company
Recovery of Leaf Area through Accelerated Shoot Ontogeny in Thrips-damaged Cotton Seedlings
1 Cotton Research Unit, CSIRO Plant Industry, Locked Bag 59, Narrabri, NSW 2390, Australia
* For correspondence. Department of Environmental Solution Technology, Faculty of Science and Technology, Ryukoku University, 1-5 Yokoba, Seta-Oe, Otsu 520-2194, Japan. E-mail tomlei{at}rins.ryukoku.ac.jp
Received: 13 October 2003; Returned for revision: 4 December 2003; Accepted: 24 March 2004, Published electronically: 21 May 2004
• Background and Aims Leaf area of cotton seedlings (Gossypium hirsutum) can be reduced by as much as 50 % by early season thrips infestations, but it is well documented that plants can regain the difference in leaf area once infestation ceases. The processes involved in the recovery have not been identified. Hypotheses include enhancement of the photosynthetic rate of the damaged leaves, more efficient leaf construction (i.e. more leaf area per unit of dry matter invested in new leaves), and more branching.
• Methods This 2-year field study examined these hypotheses and found that thrips-affected plants recovered from a 30 % reduction in total leaf area. During the recovery period, repeated measurements of gas exchange, leaf morphology and individual leaf areas at all nodes were made to assess their contribution to the recovery.
• Key Results Recovery was not achieved through the previously proposed mechanisms. The pattern of nodal development indicated that the duration of leaf expansion of the smaller deformed leaves was shorter than that of control leaves, possibly because they had fewer cells. The production and expansion of healthy upper node leaves in thrips-affected plants could, therefore, begin sooner, about 1–2·5 nodes in advance of control plants. The proposed process of recovery was evident but weaker in the second year where thrips numbers were higher.
• Conclusions It is concluded that thrips-affected plants overcame the leaf area disparity through an accelerated ontogeny of main stem leaves. By completing the expansion of smaller but normally functioning lower node leaves earlier, resources were made available to the unfolding of larger upper node leaves in advance of control plants. The generality of this mode of plant resistance in pest damage remains to be determined.
Key words: Gossypium hirsutum, cotton, leaf ontogeny, thrips damage, defoliation, leaf area recovery.
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