Authors: RINKI, VANITA PANDEY & PRIYANKA CHANDRA
Lodging is defined as the permanent displacement of shoots of small grained cereal plants from their vertical stance, which ultimately limits crop productivity. Significant research was undertaken for minimising the lodging risk, emphasising mainly on the introduction of dwarfing gene since it was observed that the tall Indian wheat varieties have a tendency to lodge upon fertilizer application. However, it is difficult to find an effective solution for lodging because it is a complex phenomenon influenced by several factors like rain, wind, soil type, topography, nutrient status of soil, previous crop etc. Two types of lodging are observed in cereals; stem lodging and root lodging where, stem lodging occurs due to breakage of lower internodes, while root lodging occurs due to poor anchorage of root system and is the most commonly observed type of lodging. Lodging is more common during grain filling stage and maturity as most of the photo assimilates move towards the upper parts of the plant and thereby makes the canopy heavier. Further, the impact of lodging depends upon plant’s phenological stage and the duration of lodging. In wheat, variable yield reduction has been recorded when lodging was imposed at ear emergence (31%), milking stage (25%), soft dough stage (20%), and hard dough stage (12%). Lodging angle also plays a significant role, higher the lodging angle lesser will be the chances of recovery as lodging interferes with water and nutrient absorption and assimilates partitioning, hence resulting in significant yield reduction. Altered red:far-red ratio because of shading effect, high humidity and anaerobic micro-environment are additional lodging induced impacts which provides favourable environment to microbial infestation.
Necessity of lodging based research
The growing population necessitates an urgent increase in crop productivity to meet the growing food demand of the future; therefore enhancing the yield potential of wheat is an effective approach in view of the current limited resources. The unpredictable weather conditions and climate change also significantly affect the crop productivity negatively. Hence, the need of the hour is to explore the effect of lodging for developing lodging resistant wheat varieties for assured agriculture production. Lodging also deteriorates grain quality by reducing grain size and grain weight thereby significantly reducing the milling quality as well. Presence of high percentage of small and poor quality grains limits its use and hence the likelihood of achieving a premium price in the market. Furthermore, the humic micro-environment around the lodged plants makes them prone to fungal infestations. Lodging is a persistent phenomenon which reduces yield up to 80% in wheat, 83.9% in rice, 65% in barley, 40% in oats and 20% in maize (Shah et al., 2016). Therefore, any programme or strategy to improve yield potential should also include lodging tolerance. The key traits for lodging tolerance of wheat plant type under Indian conditions have not been clearly identified, hence there is an urgent need to screen and identify the lodging resistance genotypes for both culm and root related characteristics. Various calibration models were also developed for wheat lodging but no single model can be accepted/ applied universally. So, modification in crop husbandry practices can be a thrust area to limit lodging induced losses.
Potential plant traits for lodging resistance
Few plant characteristics like plant height, material strength of stem base, stem diameter, wall width, centre of gravity, root spread and depth of root plate were identified for lodging tolerance in wheat ( Table 1). Biochemical components also contribute significantly for lodging tolerance. Presence of lignin, silica, cellulose and hemicelluloses played a significant role in stem strengthening (Kong et al., 2013). Lignin is a polyphenolic polymer closely linked with cellulose and hemicelluloses to provide mechanical strength and rigidity to plant culm. But, spatial distribution of these components is more important than total concentration. Some researchers also observed that the accumulation of higher concentration of starch provides more strength to culm.
Table1: Correlation of plant traits with lodging tolerance
|Plant trait||Correlation with Lodging tolerance||Reference|
|Plant height||Negative||Okuno et al., 2014|
|Internode length||Negative||XIAO et al, 2015|
|Stem solidness||Positive||Xiang et al., 2016|
|Stem/Culm diameter||Positive||XIAO et al, 2015|
|Culm wall thickness||Positive||Xiang et al., 2016|
|Number of vascular bundles||Positive||Hasnath Karim and Jahan, 2013|
|Heavy crop canopy||Negative||Wang et al., 2012|
|Stem material strength||Positive||Pinera Chavez et al., 2016|
|Tiller number||Negative||Tripathi et al., 2003|
|Lignin content||Positive||Okuno et al., 2014|
|Silicon content||Positive||Zhang et al., 2010|
|Root plate spread||Positive||Pinthus , 1967|
Agronomic practices and lodging:
Nitrogen fertilizers: Nitrogen causes lush growth and heavier canopy and higher levels of residual nitrogen at early growth stage reduces the stem strength. Subsequently, excessive stem elongation due to nitrogen can reduce stem strength.
Seed rate: High seed rate produce dense plant canopy where plants compete for light and nutrients. Shading effect due to low light penetration alters photosynthesis and restricts dry matter production. Lack of proper spacing may result in shallow dysplastic roots prone to failure of anchorage system. Reduction in number of plants within a row or increasing row-to-row spacing significantly reduces lodging risk due to production of more number of crown roots.
Sowing time: Sowing time significantly influence the lodging index in cereals. Early sowing may produce high tiller number per plants, thin and long stem with lower material strength with more base bending moments. Delay/late sowing can reduce the chance and intensity of lodging. A delay of 10-15 days can reduce lodging incidence significantly by decreasing base bending moments of the shoot in wheat.
Varietal selection: Taller varieties are more prone to lodging than the dwarf/semi dwarf ones as their centre of gravity is higher than shorter plant types.
Soil : Soil conditions also play critical role for lodging. Excess soil moisture limits root development and anchorage capacity as well. Furthermore, the rhizospheric conditions favour root rots. Soil health is an important component to produce a healthy plant population.
Irrigation: Irrigation practices significantly influence the lodging incidences in cereal crops. Flood irrigation reduces the anchorage strength of roots and a simultaneous high velocity wind may cause severe lodging. Sprinkler irrigation can induce lodging at earlier stages while drip irrigation provides an effective irrigation management system.
Plant Growth Regulators: These are synthetic compounds which reduce cell division and elongation and finally reduce plant height. Use of Plant Growth Regulators is a common practice in many developed countries. PGR’s like Uniconazole, Chlormequat Chloride, Trinexapac-ethyl, Mepiquat Chloride control stem elongation and indirectly enhance stem strength.
Hence, the following management practices can be used to reduce lodging:
- Avoid tall varieties
- Avoid high seeding rates
- Soil testing to know the fertility condition of the field
- Avoid excess use of NPK /urea
- Avoid irrigation during high wind and temperature
- Grow lodging resistant variety
- Follow crop rotation
- Follow integrated pest management practices
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About Author / Additional Info:
Rinki and Vanita Pandey are working as Scientist at ICAR-Indian Institute of Wheat and Barley Research, Karnal
Priyanka Chandra is working as scientist at ICAR-Central Soil Salinity Research Institute, Karnal