Maize (Zea mays L.) is referred to as the “Queen of cereals” and in many parts of the world maize is being used as a staple food. In India, maize is the third most important food crop after rice and wheat. It is cultivated in 90.27 lakh ha with the productivity of 3070 kg/ha (INDIASTAT, 2019). Maize is cultivated throughout the year in all states of the country for various purposes including grain, fodder, green cobs, sweet corn, baby corn, pop corn, etc. Of the total maize produced in India, approximately 47 per cent is used as poultry feed, followed by 13 per cent as livestock feed and food purpose each, 12 per cent for industrial purposes, 14 per cent in starch industry, 7 per cent as processed food and 6 per cent for export and other purposes (IIMR, 2016-19). In Tamil Nadu, it is cultivated in an area of 3.24 lakh hectare with 25.91 lakh tonnes of production during 2017-18 (INDIASTAT, 2020). About 250 insect species are associated with maize in field and storage conditions (Mathur, 1992) and with the recent introduction of the invasive fall armyworm Spodoptera frugiperda (Lepidoptera: Noctuidae) there is a growing concern among maize growers of the country (Navin et al., 2021). The fall armyworm is an insect native to tropical and subtropical regions of the Americas (Sparks, 1986; FAO, 2018). The incidence of this pest was first observed in Shivamogga, Karnataka during May, 2018 (Tippannavar et al., 2019).Among Indian states, Madhya Pradesh and Karnataka has the highest area under maize (15% each) followed by Maharashtra (10%), Rajasthan (9%), Uttar Pradesh (8%) among others. After Karnataka and Madhya Pradesh, Bihar is the highest maize producer, while Andhra Pradesh is having the highest state productivity. Some districts like Krishna, West Godavari etc. records as high as 12 t/ha productivity (IIMR, 2020). The fall armyworm larvae is a cosmopolitan (Luginbill, 1928), polyphagous pest which can feed on about 80 different plant species including crops such as corn, rice, small millets, sugarcane, alfalfa, soybean, sorghum, cotton and vegetable crops (Wiseman et al., 1966; Sparks, 1979; Pitre and Hogg 1983; Pogue, 2002; Capinera, 2008). Though this pest feeds on several crops, maize is the most preferred host. It feeds mostly on all the stages of maize, the fall armyworm larva enters into maize field as early as 13 days old crop and starts scrapping on the leaf surface initially. Within a week the 3rd instar stage start to reside inside the whorl causing extensive damage to meristamatic region of the plant (Harrison, 1986; Melo and Silva 1987). Presently, fall armyworm is kept under check through a predominantly pesticide based approach which may not be feasible in the long run. Host plant resistance seems to be an alternate option which will provide ecologically and environmentally feasible solution for managing fall armyworm. Morphological, nutritional and secondary metabolite variations among the maize hybrids influence the feeding preference of fall armyworm. The morphological plant characters viz., number of leaves/plant, leaf area, leaf trichome density, cob length and cob height above ground and nutritional properties viz., total protein content, amino acids, glucose, total non-structural carbohydrates (TNC), protein to TNC (P/C) ratio and biochemical properties viz., peroxidase and lipoxygenase activities are said to confer resistance to fall armyworm by several researchers all over the world (Paul and Deole 2020; Chen et al., 2009). Hence the present study was aimed at identifying biophysical and biochemical bases of resistance in maize inbred lines being maintained at TNAU, Coimbatore. MATERIALS AND METHODS Rearing of S. frugiperda. The life stages of fall armyworm viz., egg masses and larva were collected from the infested maize field at Department of Millets, New area, TNAU, Coimbatore (11.024˚ N latitude and 76.924˚E longitude). The different life stages were reared at fall armyworm laboratory, Department of Agricultural Entomology, TNAU, Coimbatore. Egg masses collected from corn fields were surface sterilised with a 0.02 percent sodium hypochlorite solution, dried, and stored individually in plastic jars until hatching. The neonates were moved to a larger plastic container with artificial diet after hatching. Larvae were grown in plastic jars on artificial diet from the third instar onwards until they reached the pre-pupal stage. Pupae were collected from the jar after pupation, put on sterilised petridish with cotton and kept on the cage for moth emergence. For egg-laying, these adult moths were released into an oviposition cage with 10 day old potted maize plants. The male to female moth ratio in the oviposition cage was 1:1. Adult moths were fed with a cotton swab soaked in a ten percent honey solution. Using a camel hair brush, the eggs placed on the potted maize plants were retrieved and utilised for culture multiplication. Screening of maize inbred lines. The different maize inbreds were sown in the New area of Department of Millets, TNAU, Coimbatore during Rabi 2021-2022 in a Randomized Block Design (RBD) with a row length of 2.5 cm under two replications (Table 3b). The recommended agronomic practices viz., fertilizer application, irrigation and weeding were followed scrupulously as per the crop production guide recommendation of TNAU. Artificial infestation was done manually, using a camel hair brush, with 5-10 neonates into the whorl of each plant at 21 days after emergence (Prasanna et al., 2022). Fall armyworm infestation was recorded at weekly intervals on ten randomly selected plants from each inbred starting from 7 days after emergence up to 52 days after emergence, by which time tassels would have started emerging. The fall armyworm infestation was recorded following a 1- 9 scale with different levels of whorl injury (Table 1) (Davis et al., 1996) besides following a 1-9 scale for kernel damage (Table 2) (Williams et al., 2006). After categorizing the maize inbreds as resistant/ susceptible (Table 1 & 2), a total of 13 inbreds which registered lesser score (≤ 4.0) were further selected for observation of various morphological plant characteristics. The details of maize inbreds are furnished in Table 3a. Morphological basis of resistance against Spodoptera frugiperda in maize. Different morphological plant parameters viz., number of leaves per plant, plant height (cm), leaf length (cm), leaf width (cm), leaf trichome density (no/cm2), cob height (cm) and length (cm) were recorded from the maize inbreds. Leaf length and leaf width were measured from the 3rd leaf from the top with the help of a measuring tape. Leaf trichome density was counted under a Leica microscope from 6th leaf on an area of one cm2 dia at three different points of a leaf, selected randomly and the mean trichome density was arrived and expressed as no/cm2. Cob height above the soil level and cob length was measured with the help of measuring tape up to the node position of cob. All the parameters were recorded from three plants that were randomly selected in a row. The data were subjected to ANOVA and statistically analyzed with IBM SPSS Statistics v22.0. RESULT AND DISCUSSION The data regarding fall armyworm damage recorded from 50 inbreds is furnished in Table 3. On the basis of leaf damage rating and kernel damage rating of maize BOX.NO 72173-2-1-1 recorded the minimum leaf damage (2.1), while BOX.NO 426-3 recorded the maximum leaf damage (6.6). With regard to kernel damage BOX.NO.1076-5-2-2 recorded the minimum kernel damage (1.5) while, BOX.NO 1076-5-4-1, 9119-1-2-1 and BOX.NO 426-3 recorded maximum kernel damage (5.8). Morphological characters Vs leaf damage& cob damage by S. frugiperda. Various morphological characters such as number of leaves per plant, leaf trichome density, leaf area (leaflet length and leaflet width) were correlated with leaf damage of maize by fall armyworm on 13 selected inbreds. Similarly the cob length and cob height above ground were also correlated with that of kernel damage of maize by fall armyworm (Table 5). Number of leaves/ plant. The number of leaves in 13 different inbreds varied from 7.4 to 10.4 leaves/ plant (Table 4). The maximum number of leaves was recorded in the UMI 406 (10.4) and BOX.NO. 1048-7 (10.0) which were at par with each other followed by BOX.NO.1253-8 (9.6), while minimum number of leaves was recorded in UMI 1003-2-3 (7.4). Leaf number in relation to fall armyworm can be interpreted in two ways. Higher the number of leaves, higher the surface area for fall armyworm oviposition and hence can have a direct bearing on the fall armyworm infestation (Yadav et al., 2021). On the other hand, plants being tolerant to fall armyworm tend to produce more number of leaves as a means of compensation (Ali et al., 2018). In the present investigations, number of leaves had a negative but non-significant correlation (r = -0.44) with that of leaf damage rating. Leaf area (cm2). The leaf area is one of the factor that corresponds to higher levels of infestation by fall armyworm. The leaf area in different inbreds varied from 108.2 cm2 to 398.9 cm2. The maximum leaf area (398.9 cm2) was observed in the BOX.NO.1048-7 followed by BOX.NO.1131-5 (335.4 cm2), BOX.NO.1131-1 (315.2cm2) which were at par with each other. Whereas, the minimum leaf area was observed in BOX.NO.72173-2-1-1 (108.2 cm2) (Table 4). The fall armyworm, Spodoptera frugiperda had a significant positive correlation between leaf area (cm2) and leaf damage rating. However, it was positive indicating that with increase in leaf area (cm2) there will be increase in infestation level (r = 0.64). This is in accordance with Yadav et al. (2021) where more number of broader leaves play a role in increasing the temperature of canopy as well as help in the movement of larva from plant to plant for natural egg laying besides providing more surface area. But according to Afzal et al. (2009) the leaf length and width was found to be negatively correlated with infestation by C. partellus, which is a stem borer, though. Leaf trichomedensity (No/ cm2. The leaf trichome density of 13 maize genotypes differed significantly. The trichome density in different inbreds ranged between 18.7 to 64.3 no/cm2. The maximum trichome density was observed in BOX.NO.72173-2-1-1 (64.3/cm2) followed by BOX.NO.1076-5-2-2 (46.0/ cm2) and UMI 406 (35.7/cm2), whereas, the minimum trichome density was observed in BOX.NO.1048-7 (14.45/cm2) (Table 4). The fall armyworm, Spodoptera frugiperda incidence had a highly significant negative correlation between trichome density (no/ cm2) at 45 DAS and leaf damage rating (r= -0.83). Density of trichomes plays a crucial role in plant resistance and had an influence against the chewing damage by S. frugiperda (Gustavo Moya-Raygoza et al., 2016). The trichomes also actas a barrier for feeding by fall armyworm, which could explain why resistant hybrids have lesser leaf damage (Wellso and Hoxie 1982). According to the investigations of Afzal et al. (2009) the leaf trichomes may have impeded the ingestion of plant material and may have influenced the digestion and usage of the food by the fall armyworm. Cob length (cm). The length of cob of maize showed significant difference in different genotypes. The cob length in different inbreds varied from 14.9 to 39.8. Higher cob length is one of the factor corresponds to higher level of infestation by fall armyworm. The length of cob (39.8 cm) was observed as maximum in UMI 1153, while the minimum length of cob was observed in UMI 1003-2-3 (14.9 cm), followed by UMI 406 (16.7 cm) and BOX.NO.72173-2-1-1 (17.6 cm) which were at par with each other (Table 4). There was a significant positive correlation between cob length (cm) and kernel damage rating. Thus, with increase in cob length (cm) there was increase in infestation level (r = 0.57). This is in contradiction to Ali et al. (2015) where the cob length showed a significant but negative correlation with that of pest infestation. Cob height (cm) above ground level. The height of cob above ground showed significant difference in different inbreds. The cob height above ground in different inbreds ranged from 58.7 to 120 cm. Cobs formed at a greater height is one of the factor that corresponds to higher level of infestation by fall armyworm. It was found to be maximum in BOX.NO.1048-7 (120 cm), while minimum in BOX.NO.72173-2-1-1 (61.7 cm) followed by UMI 406 (72.7 cm) and UMI 504 (73.0 cm) which were at par with each other (Table 4). The fall armyworm, Spodoptera frugiperda had a significant positive correlation between cob height above ground level (cm) and kernel damage rating. But it was positive indicating that with increase in cob height above (cm) there was increase in infestation level (r= 0.89).Cobs positioned at greater heights from ground level implies that, adult moths will find it easy to oviposit on the cobs. On the other hand, cob positioned at relatively lesser heights will not be clearly visible from above and this could be the reason for the positive correlation. But according to Kulkarni et al. (2015) the cob height was negatively correlated with Chilo partellus and Sesamia inferens infestation and the differences are found to be non- significant.