Abstract [Objective] The heat tolerance of Camellia attracts more attention due to its rich flower types
and colors and long flowering period. Suitable evaluation methods and indexes can provide bases for the
heat-tolerance identification, the discovery of heat-tolerance germplasm, and the breeding of new cultivars
of Camellia. [Methods] C. uraku and ‘Wirlinga Cascade’ were used as reference materials, and 7 new
cultivars of cluster-flowering camellia were selected as test materials. They were cut in vase. After shortterm
(5 h) or long-term (7 d) high-temperature (42 ℃/35 ℃) treatment, changes of morphological and
photosynthetic indexes were investigated and heat tolerance was evaluated comprehensively. [Results] (1)
The contents of chlorophyll, carotenoid, and chlorophyll a/b, net photosynthetic rate (Pn), and stomatal
conductance (Gs) of ‘Chuizhi Fenyu’ and ‘Wirlinga Cascade’ were increased. Their maximum photochemical
efficiency of PSⅡ (Fv/Fm ), potential activity of PSⅡ (Fv/Fo), and electron transport rate
(ETR) were remained at a high level. Additionally, they did not show signs of heat damage after 7 days of
high temperatures. Pn and Gs of ‘Jinye Fenyu’, ‘Shangzhi Huazhang’, and ‘Meigui Chun’ were decreased
significantly under high temperature stress, while intercellular CO2 concentration (Ci) was increased.
Among them, the Fv/Fm, Fv/Fo, and ETR of ‘Jinye Fenyu’ and ‘Shangzhi Huazhang’ were
significantly reduced. After 7 days of long-term high temperature stress, these 3 cultivars showed severe
heat damage or became dead. (2) 15 individual indicators were converted into 4 independent comprehensive
indicators with cumulative contribution rate of 90% through principal component analysis. The comprehensive
weight values of chlorophyll content, carotenoid content, and xanthophyll content were higher at 5
h under high temperature stress, and the comprehensive weight values of chlorophyll a/b, Fv/Fm, photochemical
quenching coefficient (qP), and non-photochemical quenching coefficient (qN) were higher at 7 d
under high temperature stress. [Conclusion] According to the comprehensive evaluation value D , ‘Chuizhi
Fenyu’ is a heat-tolerance cultivar, ‘Shangzhi Yueguangqu’, ‘Shangzhi Huanlesong’, and ‘Sweet Gem’
are moderate tolerance, and ‘Meigui Chun’, ‘Shangzhi Huazhang’, and ‘Jinye Fenyu’ are the weakest
among the new cultivars of cluster-flowering camellia. Chlorophyll, carotenoid, and xanthophyll contents can be
used as the key indicators to analyze the short-term high temperature stress, while chlorophyll a/b, Fv/Fm, qP,
and qN can be used as the key indicators to analyze the long-term high temperature stress of Camellia
