Citrus Color as Biomarker for Seasonal Health Status Indicator

As organic beings, biomarkers are always within, on and around us in everyday life. The biomarkers that I pay attention to most outside of my own body-system are often related to season/soil and agricultural biomarkers.

One such system that I care for is a Lemon-citrus tree. I transplanted this tree 5 years ago as a youngling and have maintained, monitored and pruned this tree to produce lemons of distinct and useful flavor. The breed is known as Sorrento as it is from the family of Italian lemons that of which produce the world’s tastiest Limoncelo (a refreshing, alcoholic beverage) enjoyed traditionally off the Amalfi Coast of Italy –


Each fall and spring, I attend to trimming and preparing the tree when it shows signs of adaptation to the next harvest season. Being as the “fall” and “spring” in an arid, temperate, desert climate can vary greatly from year to year, the timing for watering, fertilizing and pruning an tree or shrub can make the difference between a healthy and high volume fruit generation each season and/or a low volume and struggled fruit bearing.


Identifying with the seasonal biomarker (the sun) and it’s movement on the horizon as well as it’s intensity has suggested to me a change from the summer season to the fall. Additionally, temperatures, both in the evening as well as the afternoons have dropped significantly and are indicative of a good time for tending to the fall citrus season.

The most identifiable biomarker for citrus health and growth is the skin coloration of the fruit. The color tone ultimately provides a cue regarding it’s water allocation, soil condition and sun exposure.

In the below example, you can see where the discoloration of the fruit is suggesting a ripening fruit, it is also showing pale signs of yellow vs. a vibrant and healthy “lemony”  yellow. This is a biomarker for early(pre season) fruit development.

Ripened lemon fruit, too early and appearance is thin and underdeveloped.
Unripened lemon fruit looking healthy and plump

A green lemon suggests it is unripened. The vibrancy, and plumpness of this fruit suggests a future ideal lemon is possible here.  These visual “biomarkers” are critical for my ability to maintain and harvest a healthy batch of lemons this year. Albeit, not for Limoncelo (this time), rather for a nice fat lemon cake (see Food Science experiment).

Additionally, I have discovered that the current interest is in respect to identifying diseases in trees using biomarker, genetic and scientific methods:

1) Report of Suggestions on Florida’s Asymptomatic infected trees –

2) Point-of-use nanosensor for detection of citrus greening disease (Huanglongbing) –

It would appear as though some technology exists for identifying citrus health by using computer vision as well as other technologies. Perhaps one could be developed for home gardening use? I also like the idea of designing an infographic for citrus health monitoring as in:

Perhaps one is needed for citrus in AZ?

Bio indicators

Since I’m still new to Phoenix, I have interviewed one of my friends, a resident in Phoenix since birth to get an idea about local bio indicators. She mentioned about the activities of mosquitoes as an indication of rain. According to her, mosquitoes come out noticeably in numbers few hours before a rain. Personally I have neither experienced this in last two months here in Phoenix nor in places I lived before.

But I have a similar experience in Sri Lanka with a bird species called Hirundo rustica. In singhalese we call it “wahi-lihiniya” which means rain bird. They started to fly as groups indicating a rain is coming soon. According to my experience this is kind of a reliable indication.

Further, I have gone through a scholarly article on using  Ant groups as bioindicators of Forest Health in Northern Arizona Ponderosa Pine Forests. According to them the size, kind and the activities of the ant groups can be used as indicators to measure the severity of the disturbances happened to the forest eco system as results of wildfires.

Unfortunately I was unable to experience any bio indicators specific to the Phoenix area by my self yet.

Queen of the Equinox

Cereus hildmannianus is one of several similar species of organ pipe cactus that found in South America, California and Arizona. These medium-sized cacti are nearly spineless and bloom selectively for only a few nights a year. The flowers unfold from a pod and bloom one evening, then shrivel into a fruit the next day. Used as a natural sensor they could guide desert  farmers in planting crops such as corn, squash and beans for a spring harvest or for planting melons at the spring equinox. Analog methods of detection could include planting as hedges (it can grow prolifically) and using the Mk. 1 eyeball for approximating the equinox. This could have worked for Hohokam farmers without access to astronomer-priests. A digital system might use a low-resolution camera and use a prior distribution or frame referencing image processing technique to trigger scripted remote events.

While it’s cousin species only flower synchronously one night a year, it flowers over several nights. It has less fragrant blossoms and they shrink into a dragonfruit-like fruit. These cacti seem to display a biological light switch using a technique known as photomorphogenesis that is triggered by the plant’s photochrome system.

According to Devlin, Christie & Terry (2007) “timing of flowering in many species is governed by light. In this case, duration of light is the important factor. Lengthening days (or more strictly shortening nights) signal the approach of spring while shortening days (lengthening nights) signal the approach of winter. This regulation of flowering by light is mediated through interaction with an internal 24 h timekeeper known as the circadian clock to ensure that the flowering process is receptive to light during the evening.” This is dramatically expressed in C. hildmannianus.

Equipment: Canon T3, tripod, Polaroid timer, miscellaneous cameras.

Music is Ghosts I, 6 by NIN, Open Content License.