Intermittent versus continuous drought: chlorophyll a fluorescence reveals photosystem resilience in tomato

Jesús Daniel Peco¹Ana Centeno²Rubén Moratiel²Jaime Villena¹Marta María Moreno¹Jesús Antonio López¹David Pérez-López^2*

• ¹Escuela Técnica Superior de Ingenieros Agrónomos - CR, Universidad de Castilla-La Mancha, Ciudad Real, Spain
• ²Universidad Politecnica de Madrid Escuela Tecnica Superior de Ingenieria Agronomica Alimentaria y de Biosistemas, Madrid, Spain

ABSTRACT Recurrent drought threatens Mediterranean tomato yields, yet its time‑scale effects on photochemical tolerance remain unclear. Our objective was to investigate how drought duration affects photochemical tolerance in three commercial cultivars ('Sintonía', 'Marejada', 'Valenciano') and three Mediterranean landraces ('82', '264', '260') under glasshouse conditions. Plants underwent either two short water‑stress pulses (WS1) or one deficit (WS2) before rewatering. Stem water potential dropped to −1.6 MPa in both regimes. We monitored chlorophyll a fluorescence (OJIP test), leaf chlorophyll and gas exchange. The first WS1 pulse transiently increased performance index (PIABS) and electron‑transport efficiencies (ΨE0, ϕE0) by 20–40 % in four cultivars. Photosynthesis declined by –70 to –80 % but recovered within three days of irrigation. 'Sintonía' showed early increases in dissipation (ϕD0) and fluxes (ABS/CS0, DI0/CS0), while maximum quantum yield (ϕP0) remained unchanged across genotype. Sustained WS2, however, reduced PIABS and ϕP0 by –18 to –50 %, increased ϕD0, ABS/CS0 and DI0/CS0 by 30–60 % in all except '260', whose OJIP profile remained stable. Photosynthesis dropped near zero but recovered in five genotypes; '264' recovered only 50 %, showing irreversible damage. Chlorophyll content stayed constant, so shifts were pigment‑independent. These responses define a three‑stage resilience model: (i) reversible photoprotective adjustment to short severe drought; (ii) cumulative photochemical damage during sustained deficit; and (iii) genotype‑dependent recovery. OJIP indices thus reflect stress duration as well as genotype. Combining temporal stress integrals with OJIP screening provides a robust pipeline for breeding Mediterranean tomatoes adapted to future drought, advancing knowledge of drought resilience mechanisms.