Effects of kaolin on gas exchange, yield and head atrophy of artichoke, Cynara cardunculus L. subsp. scolymus (L.) Hayek

Environmental stress, as high air temperature and low relative humidity, increases the evaporative demand of the atmosphere, drives the sap flow mainly towards the leaves and causes a calcium deficiency in the artichoke heads that often promotes the formation of atrophic heads. The hypothesis is that conditions leading to a reduction of leaf temperature and transpiration can contribute to reduce the Ca deficiency-related disorders. Therefore, the use of kaolin-based particle film could be an effective tool as antitranspirant, thus mitigating detrimental effect of high evaporative demand that leads to the head atrophy. This study has investigated the effects of kaolin on gas exchange, yield and head atrophy of artichoke 'Violetto di Provenza', during June 2009-May 2010 in field conditions (southern Italy). The following treatments were compared: control without kaolin (C); kaolin sprayed plants starting 60 days (K1) and 67 days (K2) after the awakening. Kaolin, overall, at leaf scale caused the reduction, respectively by 10.3 and 23.8% in assimilation rate and transpiration, which led to 17.9% increase in photosynthetic water use efficiency. The production of marketable heads and atrophic heads not changed with kaolin application. The atrophic heads, all produced in the first three harvests, were 1,635 and 1,346 ha-1, respectively in C and K treatments, corresponding to 51.0 and 44.1% of total yield obtained in the same harvests. This does not exclude that kaolin can reduce heads atrophy, since the excessive earliness in artichoke awakening (mid-June), might have placed the crop in extreme climatic conditions, not sufficiently 'mitigated' from kaolin. Less extreme climatic conditions, which normally occur by awakening the artichoke later, could instead be mitigated by kaolin. Therefore, it would be useful to repeat the trial by scheduling artichoke awakening in different periods.