Photoperiodic Flowering Response of Essential Oil, Grain, and Fiber Hemp (Cannabis sativa L.) Cultivars

Cultivation of hemp (Cannabis sativa L.) in tropical and subtropical regions can be challenging if the flowering behavior of a given cultivar is unknown, poorly understood, or not accurately selected for the photoperiod. Identifying cultivars adapted to local environmental conditions is key to optimizing hemp vegetative and flowering performance. We investigated the effects of varying light cycles in regulating extension growth and flowering response of 15 essential oil and 12 fiber/grain hemp cultivars both indoors and outdoors. Plants were subjected to 11 photoperiods in the controlled rooms ranging from 12 to 18 h, and natural day length in the field. The critical photoperiod threshold was identified for seven essential oil cultivars and two fiber/grain cultivars. “Cherry Wine-CC,” “PUMA-3,” and “PUMA-4” had the shortest critical day length between 13 h 45 min and 14 h. The flowering of essential oil cultivars was generally delayed by 1–2 days when the photoperiod exceeded 13 h compared with 12 h, and flowering was further delayed by 7–8 days when the photoperiod exceeded 14 h. In fiber/grain cultivars, flowering was generally delayed by 1–3 days when the day length exceeded 14 h. Flowering for most essential oil cultivars was delayed by 5–13 days under a 14-h photoperiod compared with 13 h 45 min, suggesting a photoperiod difference as little as 15 min can significantly influence the floral initiation of some essential oil cultivars. Cultivars represented by the same name but acquired from different sources can perform differently under the same environmental conditions, suggesting genetic variation among cultivars with the same name. Average days to flower of fiber/grain cultivars was correlated with reported cultivar origin, with faster flowering occurring among northern cultivars when compared with southern cultivars. Plant height generally increased as the day length increased in essential oil cultivars but was not affected in fiber/grain cultivars. In addition, civil twilight of ~2 μmol·m−2·s−1 was discovered to be biologically effective in regulating hemp flowering. Collectively, we conclude that most of the essential oil cultivars and some southern fiber/grain cultivars tested express suitable photoperiods for tropical and sub-tropical region cultivation.

Photoperiodic Flowering Response of Essential Oil, Grain, and Fiber Hemp (Cannabis sativa L.) Cultivars

Cultivation of hemp (Cannabis sativa L.) in tropical and subtropical regions can be challenging if flowering behavior of a given cultivar is unknown, poorly understood, or not accurately selected for the photoperiod. Identifying cultivars adapted to local environmental conditions is key to optimizing hemp vegetative and flowering performance. We investigated the effects of varying light cycles in regulating extension growth and flowering response of 15 essential oil and 12 fiber/grain hemp cultivars both in indoors and outdoors. Plants were subjected to eleven photoperiods in the controlled rooms ranging from 12 h to 18 h, and natural day length in the field. The critical photoperiod threshold was identified for seven essential oil cultivars and two fiber/grain cultivars. 'Cherry Wine-CC', 'PUMA-3', and 'PUMA-4' had the shortest critical day length between 13 h 45 min and 14 h. The flowering of essential oil cultivars was generally delayed by 1 to 2 d when photoperiod exceeded 13 h compared to 12 h, and flowering was further delayed by 7 to 8 d when photoperiod exceed 14 h. In fiber/grain cultivars, flowering was generally delayed by 1 to 3 d when day length exceeded 14 h. Flowering for most essential oil cultivars was delayed by 5 to 13 d under 14 h photoperiod compared to 13 h 45 min, suggesting a photoperiod difference as little as 15 min can significantly influence the floral initiation of some essential oil cultivars. Cultivars represented by the same name but acquired from different sources can perform differently under the same environmental conditions, suggesting genetic variation among cultivars with the same name. Average days to flower of fiber/grain cultivars was correlated with reported cultivar origin with faster flowering occurring among northern cultivars when compared to southern cultivars. Plant height generally increased as the day length increased in essential oil cultivars but was not affected in fiber/grain cultivars. In addition, civil twilight of approximately 2 μmol m^-2 s^-1 was discovered to be biologically effective in regulating hemp flowering. Collectively, we conclude that most of the essential oil cultivars and some southern fiber/grain cultivars tested express suitable photoperiods for tropical and sub-tropical region cultivation.

PENGATURAN PEMBUNGAAN TANAMAN JAMBU BIJI (Psidium guajava L.) ‘KRISTAL’ MELALUI APLIKASI WAKTU STRANGULASI YANG BERBEDA

<p align="center"><strong>ABSTRACT</strong></p><p align="center"><strong><em> </em></strong></p><p><strong><em>Arrangement of Guava Flowering </em></strong><strong><em>(Psidium</em></strong><strong><em> g</em></strong><strong><em>uajava</em></strong><strong><em> </em></strong><strong><em>L.</em></strong><strong><em>)</em></strong><strong><em> ‘Krystal’ through the Application of Different Strangulation Times. </em></strong>The seasonal production of guava (<em>Psidium guajava</em>) requires flowering manipulation technique such strangulation in order to be available throughout the years. This study aimed to explain the relationship between strangulation time, the period of flowering and harvesting of guava cv 'Krystal'. The experiment was conducted from February to December 2017, in Cikabayan experimental garden of IPB University, Bogor, Indonesia. The experiment used a completely randomized design with single factor, i.e strangulation times that consisted of control (no strangulation), strangulation in March, in April and in May. The results showed that strangulation treatment was able to accelerate the emergence of flowers and increase the number of generative shoots, the number of flowers per tree and the number of fruits harvested. The increase of flowering response on strangulated trees was supported by a higher leaf C/N compared to control, which is related to the low leaf N content in strangulation treatments. The strangulation treatment could accelerate the time of flower emergence six days earlier than control.<em> </em><strong><em></em></strong></p><p><strong>Key</strong><strong>word<em>s</em></strong>: <em>guava, </em><em>C/N, flowering induction, ringing, seasonal production</em><strong><em></em></strong></p><p align="center"><strong> </strong></p><p align="center"><strong>ABSTRAK</strong></p><p align="center"><strong> </strong></p><p>Produksi buah jambu biji (<em>Psidium guajava</em>) yang bersifat musiman memerlukan teknik pengaturan pembungaan agar dapat tersedia sepanjang tahun. Penelitian ini bertujuan untuk menjelaskan keterkaitan antara waktu strangulasi dengan pola pembungaan dan panen buah jambu biji ‘Kristal’. Percobaan dilaksanakan mulai Februari sampai Desember 2017, di Kebun Percobaan Cikabayan IPB Bogor. Rancangan yang digunakan adalah Rancangan Acak Lengkap (RAL) dengan faktor tunggal yaitu waktu strangulasi yang terdiri dari 4 (empat) taraf, yakni tanpa strangulasi, strangulasi bulan Maret, strangulasi bulan April dan strangulasi bulan Mei. Hasil penelitian menunjukkan bahwa perlakuan strangulasi mampu mempercepat munculnya bunga dan meningkatkan jumlah tunas generatif, jumlah bunga per pohon, jumlah bakal buah per pohon dan jumlah buah yang dipanen. Peningkatan respon pembungaan akibat strangulasi didukung oleh C/N daun yang lebih tinggi dibandingkan tanpa stangulasi, yang berhubungan dengan rendahnya kandungan nitrogen daun pada perlakuan strangulasi. Perlakuan strangulasi mampu mempercepat waktu muncul bunga 6 hari lebih cepat dibandingkan tanpa strangulasi.</p><p><strong>Kata </strong><strong>k</strong><strong>unci: </strong>jambu biji, C/N, induksi pembungaan, pencekikan batang, produksi musiman</p>

Flowering of Blandfordia grandiflora (Christmas bells) in response to fire frequency and temperature

Blandfordia grandiflora (Blandfordiaceae) is a resprouting perennial herb in wet heathland of coastal and tableland habitats on mainland eastern Australia. It has attractive turbinate flowers of considerable horticultural value. Blandfordia grandiflora is reported to have an enhanced flowering response in the first post-fire flowering season, and management prescriptions advocate frequent fire as beneficial for the species. Nonetheless, the present study appears to be the first to document the flowering response and fate of individual plants exposed to a range of fire frequencies (3-, 6- and 9-year intervals) over an extended period. We also examined the flowering response in unburnt habitat. High survival rates (&gt;95%) were observed for B. grandiflora plants in heathland that had remained unburnt for a minimum of 30 years. Flowering after experimental burns was found to peak in the second post-fire flowering season rather than the first, and there was no clear fire frequency effect. Maximum levels of flowering during the second post-fire season reached 38 to 56% of individuals, although in some years post-fire flowering during this peak season was as low as 23%. Comparatively few plants flowered during the second-year peak season after every fire, and ~34% of individuals in both the 6- and 9-year burn treatments failed to flower at any time. Inter-fire flowering was also observed, and in some instances this flowering was not significantly different to the level achieved during the peak post-fire flowering season. For example, ~9% of individuals flowered 5–7 times over a 12-year period despite being burnt on only four occasions. Flowering after vernalisation (winter-chilling) was observed in unburnt heathland, and the level of this response was not significantly different to peak post-fire flowering in some years. The findings are examined in the context of evolutionary and habitat processes within a climate change framework. Future studies should focus on the complex interactions between climate, fire and soil for not only B. grandiflora, but more importantly for the diverse assemblage of plant species in wet heathland.