Identification of Physiological Disorder Symptoms in Lilies and Their Prevention and Control Methods
Physiological disorders, also known as non-infectious diseases, refer to the disruption of normal physiological metabolic functions in the plant itself caused by factors other than pathogens. The causes of physiological disorders may be internal factors such as mineral element deficiency, tissue aging, or environmental factors such as temperature, light intensity, and abnormal gas composition.
I. Leaf scorch
The typical symptom of leaf scorch is the formation of semicircular necrosis at the tip and margin of the leaf, sometimes also manifested as chlorosis or necrosis at the leaf margin, or yellow-green spots appearing on parts of unexpanded or expanded young leaves, and sometimes white spots as well.
On the top leaves of Asiatic hybrid lilies, ring-shaped whitening symptoms are often observed; on Oriental hybrid lilies, damage occurs even before the leaves unfold, with visible constriction in the middle of the leaf, and symptoms ranging from whitening spots to browning spots. If leaf scorch is mild, the plant can still grow; if severe enough that whitening spots become brown spots, the leaf at that location will curl; in more severe cases, all leaves and young flower buds will be damaged, and the plant will stop growing.
Since no pathogenic bacteria can be isolated from scorched leaves, it is generally believed that it may be related to fluoride pollution and low pH. It is thought that avoiding the application of fluoride contamination sources such as superphosphate fertilizer and controlling pH to 6.0-7.0 can prevent the occurrence of leaf scorch.
Generally speaking, when nitrogen fertilizer is excessive, moisture is too high, root growth is poor, soil salt content is high, and stem and leaf growth exceeds root development, the incidence of leaf scorch increases, and large bulbs are more prone to leaf scorch symptoms than small bulbs.
Methods for preventing leaf scorch include:
1. Do not choose sensitive varieties; if they cannot be avoided, do not choose the more sensitive large bulbs.
2. Moisten the soil before planting, select bulbs with a good root system, and plant them deeply.
3. On sunny days, use shading or sprinkling water to promote transpiration, and carry out proper water control during periods of increased sensitivity, prevent the spread of higher greenhouse temperature and air humidity, and try to maintain relative humidity at around 75%.
4. Rapid growth should be avoided as much as possible. For sensitive Asiatic lily hybrids, during the first four weeks, the greenhouse temperature needs to be maintained at 10-12°C; for Oriental lily hybrids, during the first six weeks, the greenhouse temperature must be maintained at 15°C.
5. Pay attention to fertilization, especially avoiding contamination containing fluoride, and adjust pH and EC values so that pH reaches above 6.
6. Pests and diseases that damage the roots should be effectively controlled.
II. Blind buds, bud abortion, and bud drop
The causes of blind buds, bud abortion, and bud drop are mainly related to variety, bulb pre-treatment, and cultivation temperature and light intensity. Generally speaking, the longer forced-dormancy refrigerated bulbs are stored, the higher the probability of blind buds, bud abortion, and bud drop occurring after planting.
For Asiatic lilies, if temperature is not well controlled during long-term storage or extended storage and transport, causing stem elongation and flower bud differentiation before planting, and if the shortened stem protrudes more than several centimeters above the bulb before planting, or if planting is delayed, problems such as blind buds, bud drop, and inhibited internode elongation will be caused. When high temperatures (above 25°C) are encountered in the early stage of flower bud differentiation, not only is the number of flowers reduced, but blind buds or bud abortion are also prone to occur. In particular, the upper temperature limit for most Asiatic lily varieties is 28°C; at 30°C, bud drop is severe, and at temperatures above 30°C, blind buds will occur. The same applies to Lilium longiflorum; when cultivated at temperatures above 30°C, flower buds stop developing at around 3 mm, resulting in poorly developed individuals.
Generally speaking, the effect of low temperature in the early stage of flower bud differentiation is still small. Once buds emerge but have not yet fully developed, encountering low temperature easily causes bud abortion or bud drop. For Lilium longiflorum, flower buds of about 1 cm or less exposed to a night temperature of 8°C will undergo bud abortion after 20 days; when flower buds are 2 cm and encounter a low temperature of around 9°C, the flower buds develop poorly and abnormal flowers increase; while flower buds of 6 cm or more, even if maintained at a daytime temperature of 13°C and a night temperature of 0°C, will not show abnormal phenomena after 40 days. In other words, from bud emergence until flower buds reach 6 cm, if low temperature is encountered, abnormal flowers are likely to occur; therefore, temperature management during this period is particularly important.
Therefore, to prevent failure of flower bud differentiation and development, excessive forced storage of bulbs should be avoided, and sprouted bulbs should not be planted at more than 3 cm. During the cultivation period, try to maintain a daytime temperature below 25°C and a night temperature of 15°C, avoiding high temperatures above 25°C and strong light. For Asiatic varieties sensitive to high temperatures, cooling facilities are needed for summer planting, such as evaporative cooling systems and shading, to control the temperature below 28°C, which can effectively reduce the bud drop rate. As for ethylene gas pollution, including excessive ethylene production caused by stress that leads to bud drop, ethylene inhibitors can be applied to reduce the bud drop problem (Mason, 1991). Alternatively, breeding efforts can be directed toward selecting varieties resistant to stress.
III. Sunscald
Sunscald refers to the phenomenon of being scorched by sunlight. It generally occurs on leaves and flower buds. When dew or irrigation water has not yet dried, under strong sunlight, the cells of plant tissues die due to high temperature. Symptoms on leaf tissue often appear as uniform whitening on the sun-facing side, while on flower buds they appear as browning scorch marks on the sun-facing side. The preventive method is to install shade nets. Do not carry out sprinkler irrigation under strong sunlight.
IV. Micronutrient deficiency